feat(meta): separate flac meta process

algo/common/dispatch.go

@@ -29,6 +29,7 @@ func RegisterDecoder(ext string, noop bool, dispatchFunc NewDecoderFunc) {
 	DecoderRegistry[ext] = append(DecoderRegistry[ext],
 		decoderItem{noop: noop, decoder: dispatchFunc})
 }
+
 func GetDecoder(filename string, skipNoop bool) (rs []NewDecoderFunc) {
 	ext := strings.ToLower(strings.TrimLeft(filepath.Ext(filename), "."))
 	for _, dec := range DecoderRegistry[ext] {

algo/common/interface.go

@@ -5,6 +5,10 @@ import (
 	"io"
 )
 
+type StreamDecoder interface {
+	Decrypt(buf []byte, offset int)
+}
+
 type Decoder interface {
 	Validate() error
 	io.Reader
@@ -14,12 +18,12 @@ type CoverImageGetter interface {
 	GetCoverImage(ctx context.Context) ([]byte, error)
 }
 
-type Meta interface {
+type AudioMeta interface {
 	GetArtists() []string
 	GetTitle() string
 	GetAlbum() string
 }
 
-type StreamDecoder interface {
-	Decrypt(buf []byte, offset int)
+type AudioMetaGetter interface {
+	GetAudioMeta(ctx context.Context) (AudioMeta, error)
 }

algo/common/meta.go

@@ -0,0 +1,50 @@
+package common
+
+import (
+	"path"
+	"strings"
+)
+
+type filenameMeta struct {
+	artists []string
+	title   string
+	album   string
+}
+
+func (f *filenameMeta) GetArtists() []string {
+	return f.artists
+}
+
+func (f *filenameMeta) GetTitle() string {
+	return f.title
+}
+
+func (f *filenameMeta) GetAlbum() string {
+	return f.album
+}
+
+func ParseFilenameMeta(filename string) (meta AudioMeta) {
+	partName := strings.TrimSuffix(filename, path.Ext(filename))
+	items := strings.Split(partName, "-")
+	ret := &filenameMeta{}
+
+	switch len(items) {
+	case 0:
+		// no-op
+	case 1:
+		ret.title = strings.TrimSpace(items[0])
+	default:
+		ret.title = strings.TrimSpace(items[len(items)-1])
+
+		for _, v := range items[:len(items)-1] {
+			artists := strings.FieldsFunc(v, func(r rune) bool {
+				return r == ',' || r == '_'
+			})
+			for _, artist := range artists {
+				ret.artists = append(ret.artists, strings.TrimSpace(artist))
+			}
+		}
+	}
+
+	return ret
+}

algo/common/meta_test.go

@@ -0,0 +1,38 @@
+package common
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseFilenameMeta(t *testing.T) {
+
+	tests := []struct {
+		name     string
+		wantMeta AudioMeta
+	}{
+		{
+			name:     "test1",
+			wantMeta: &filenameMeta{title: "test1"},
+		},
+		{
+			name:     "周杰伦 - 晴天.flac",
+			wantMeta: &filenameMeta{artists: []string{"周杰伦"}, title: "晴天"},
+		},
+		{
+			name:     "Alan Walker _ Iselin Solheim - Sing Me to Sleep.flac",
+			wantMeta: &filenameMeta{artists: []string{"Alan Walker", "Iselin Solheim"}, title: "Sing Me to Sleep"},
+		},
+		{
+			name:     "Christopher,Madcon - Limousine.flac",
+			wantMeta: &filenameMeta{artists: []string{"Christopher", "Madcon"}, title: "Limousine"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if gotMeta := ParseFilenameMeta(tt.name); !reflect.DeepEqual(gotMeta, tt.wantMeta) {
+				t.Errorf("ParseFilenameMeta() = %v, want %v", gotMeta, tt.wantMeta)
+			}
+		})
+	}
+}

algo/ncm/meta.go

@@ -6,12 +6,17 @@ import (
 	"unlock-music.dev/cli/algo/common"
 )
 
-type RawMeta interface {
-	common.Meta
+type ncmMeta interface {
+	common.AudioMeta
+
+	// GetFormat return the audio format, e.g. mp3, flac
 	GetFormat() string
+
+	// GetAlbumImageURL return the album image url
 	GetAlbumImageURL() string
 }
-type RawMetaMusic struct {
+
+type ncmMetaMusic struct {
 	Format        string          `json:"format"`
 	MusicID       int             `json:"musicId"`
 	MusicName     string          `json:"musicName"`
@@ -28,10 +33,11 @@ type RawMetaMusic struct {
 	TransNames    []interface{}   `json:"transNames"`
 }
 
-func (m RawMetaMusic) GetAlbumImageURL() string {
+func (m *ncmMetaMusic) GetAlbumImageURL() string {
 	return m.AlbumPic
 }
-func (m RawMetaMusic) GetArtists() (artists []string) {
+
+func (m *ncmMetaMusic) GetArtists() (artists []string) {
 	for _, artist := range m.Artist {
 		for _, item := range artist {
 			name, ok := item.(string)
@@ -43,22 +49,23 @@ func (m RawMetaMusic) GetArtists() (artists []string) {
 	return
 }
 
-func (m RawMetaMusic) GetTitle() string {
+func (m *ncmMetaMusic) GetTitle() string {
 	return m.MusicName
 }
 
-func (m RawMetaMusic) GetAlbum() string {
+func (m *ncmMetaMusic) GetAlbum() string {
 	return m.Album
 }
-func (m RawMetaMusic) GetFormat() string {
+
+func (m *ncmMetaMusic) GetFormat() string {
 	return m.Format
 }
 
 //goland:noinspection SpellCheckingInspection
-type RawMetaDJ struct {
+type ncmMetaDJ struct {
 	ProgramID          int          `json:"programId"`
 	ProgramName        string       `json:"programName"`
-	MainMusic          RawMetaMusic `json:"mainMusic"`
+	MainMusic          ncmMetaMusic `json:"mainMusic"`
 	DjID               int          `json:"djId"`
 	DjName             string       `json:"djName"`
 	DjAvatarURL        string       `json:"djAvatarUrl"`
@@ -80,32 +87,32 @@ type RawMetaDJ struct {
 	RadioPurchaseCount int          `json:"radioPurchaseCount"`
 }
 
-func (m RawMetaDJ) GetArtists() []string {
+func (m *ncmMetaDJ) GetArtists() []string {
 	if m.DjName != "" {
 		return []string{m.DjName}
 	}
 	return m.MainMusic.GetArtists()
 }
 
-func (m RawMetaDJ) GetTitle() string {
+func (m *ncmMetaDJ) GetTitle() string {
 	if m.ProgramName != "" {
 		return m.ProgramName
 	}
 	return m.MainMusic.GetTitle()
 }
 
-func (m RawMetaDJ) GetAlbum() string {
+func (m *ncmMetaDJ) GetAlbum() string {
 	if m.Brand != "" {
 		return m.Brand
 	}
 	return m.MainMusic.GetAlbum()
 }
 
-func (m RawMetaDJ) GetFormat() string {
+func (m *ncmMetaDJ) GetFormat() string {
 	return m.MainMusic.GetFormat()
 }
 
-func (m RawMetaDJ) GetAlbumImageURL() string {
+func (m *ncmMetaDJ) GetAlbumImageURL() string {
 	if strings.HasPrefix(m.MainMusic.GetAlbumImageURL(), "http") {
 		return m.MainMusic.GetAlbumImageURL()
 	}

algo/ncm/ncm.go

@@ -41,7 +41,7 @@ type Decoder struct {
 
 	metaRaw  []byte
 	metaType string
-	meta     RawMeta
+	meta     ncmMeta
 	cover    []byte
 }
 
@@ -172,10 +172,10 @@ func (d *Decoder) readCoverData() error {
 func (d *Decoder) parseMeta() error {
 	switch d.metaType {
 	case "music":
-		d.meta = new(RawMetaMusic)
+		d.meta = new(ncmMetaMusic)
 		return json.Unmarshal(d.metaRaw, d.meta)
 	case "dj":
-		d.meta = new(RawMetaDJ)
+		d.meta = new(ncmMetaDJ)
 		return json.Unmarshal(d.metaRaw, d.meta)
 	default:
 		return errors.New("unknown ncm meta type: " + d.metaType)
@@ -232,8 +232,8 @@ func (d *Decoder) GetCoverImage(ctx context.Context) ([]byte, error) {
 	return d.cover, nil
 }
 
-func (d *Decoder) GetMeta() common.Meta {
-	return d.meta
+func (d *Decoder) GetAudioMeta(_ context.Context) (common.AudioMeta, error) {
+	return d.meta, nil
 }
 
 func init() {

algo/qmc/client/base.go

@@ -0,0 +1,146 @@
+package client
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+type QQMusic struct {
+	http *http.Client
+}
+
+func (c *QQMusic) rpcDoRequest(ctx context.Context, reqBody any) ([]byte, error) {
+	reqBodyBuf, err := json.Marshal(reqBody)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcDoRequest] marshal request: %w", err)
+	}
+
+	const endpointURL = "https://u.y.qq.com/cgi-bin/musicu.fcg"
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+		endpointURL+fmt.Sprintf("?pcachetime=%d", time.Now().Unix()),
+		bytes.NewReader(reqBodyBuf),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcDoRequest] create request: %w", err)
+	}
+
+	req.Header.Set("Accept", "*/*")
+	req.Header.Set("Accept-Language", "zh-CN")
+	req.Header.Set("User-Agent", "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)")
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	// req.Header.Set("Accept-Encoding", "gzip, deflate")
+
+	reqp, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcDoRequest] send request: %w", err)
+	}
+	defer reqp.Body.Close()
+
+	respBodyBuf, err := io.ReadAll(reqp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcDoRequest] read response: %w", err)
+	}
+
+	return respBodyBuf, nil
+}
+
+type rpcRequest struct {
+	Method string `json:"method"`
+	Module string `json:"module"`
+	Param  any    `json:"param"`
+}
+
+type rpcResponse struct {
+	Code    int    `json:"code"`
+	Ts      int64  `json:"ts"`
+	StartTs int64  `json:"start_ts"`
+	TraceID string `json:"traceid"`
+}
+
+type rpcSubResponse struct {
+	Code int             `json:"code"`
+	Data json.RawMessage `json:"data"`
+}
+
+func (c *QQMusic) rpcCall(ctx context.Context,
+	protocol string, method string, module string,
+	param any,
+) (json.RawMessage, error) {
+	reqBody := map[string]any{protocol: rpcRequest{
+		Method: method,
+		Module: module,
+		Param:  param,
+	}}
+
+	respBodyBuf, err := c.rpcDoRequest(ctx, reqBody)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] do request: %w", err)
+	}
+
+	// check rpc response status
+	respStatus := rpcResponse{}
+	if err := json.Unmarshal(respBodyBuf, &respStatus); err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] unmarshal response: %w", err)
+	}
+	if respStatus.Code != 0 {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] rpc error: %d", respStatus.Code)
+	}
+
+	// parse response data
+	var respBody map[string]json.RawMessage
+	if err := json.Unmarshal(respBodyBuf, &respBody); err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] unmarshal response: %w", err)
+	}
+
+	subRespBuf, ok := respBody[protocol]
+	if !ok {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] sub-response not found")
+	}
+
+	subResp := rpcSubResponse{}
+	if err := json.Unmarshal(subRespBuf, &subResp); err != nil {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] unmarshal sub-response: %w", err)
+	}
+
+	if subResp.Code != 0 {
+		return nil, fmt.Errorf("qqMusicClient[rpcCall] sub-response error: %d", subResp.Code)
+	}
+
+	return subResp.Data, nil
+}
+
+func (c *QQMusic) downloadFile(ctx context.Context, url string) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, fmt.Errorf("qmc[downloadFile] init request: %w", err)
+	}
+
+	//req.Header.Set("Accept", "image/webp,image/*,*/*;q=0.8") // jpeg is preferred to embed in audio
+	req.Header.Set("Accept-Language", "zh-CN,zh;q=0.8,en-US;q=0.6,en;q=0.5;q=0.4")
+	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.47.134 Safari/537.36 QBCore/3.53.47.400 QQBrowser/9.0.2524.400")
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("qmc[downloadFile] send request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("qmc[downloadFile] unexpected http status %s", resp.Status)
+	}
+
+	return io.ReadAll(resp.Body)
+}
+
+func NewQQMusicClient() *QQMusic {
+	return &QQMusic{
+		http: &http.Client{
+			Timeout: 10 * time.Second,
+		},
+	}
+}

algo/qmc/client/cover.go

@@ -0,0 +1,21 @@
+package client
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+)
+
+func (c *QQMusic) AlbumCoverByID(ctx context.Context, albumID int) ([]byte, error) {
+	u := fmt.Sprintf("https://imgcache.qq.com/music/photo/album/%s/albumpic_%s_0.jpg",
+		strconv.Itoa(albumID%100),
+		strconv.Itoa(albumID),
+	)
+	return c.downloadFile(ctx, u)
+}
+
+func (c *QQMusic) AlbumCoverByMediaID(ctx context.Context, mediaID string) ([]byte, error) {
+	// original: https://y.gtimg.cn/music/photo_new/T002M000%s.jpg
+	u := fmt.Sprintf("https://y.gtimg.cn/music/photo_new/T002R500x500M000%s.jpg", mediaID)
+	return c.downloadFile(ctx, u)
+}

algo/qmc/client/search.go

@@ -0,0 +1,52 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+)
+
+type searchParams struct {
+	Grp         int    `json:"grp"`
+	NumPerPage  int    `json:"num_per_page"`
+	PageNum     int    `json:"page_num"`
+	Query       string `json:"query"`
+	RemotePlace string `json:"remoteplace"`
+	SearchType  int    `json:"search_type"`
+	//SearchID    string `json:"searchid"` // todo: it seems generated randomly
+}
+
+type searchResponse struct {
+	Body struct {
+		Song struct {
+			List []*TrackInfo `json:"list"`
+		} `json:"song"`
+	} `json:"body"`
+	Code int `json:"code"`
+}
+
+func (c *QQMusic) Search(ctx context.Context, keyword string) ([]*TrackInfo, error) {
+
+	resp, err := c.rpcCall(ctx,
+		"music.search.SearchCgiService",
+		"DoSearchForQQMusicDesktop",
+		"music.search.SearchCgiService",
+		&searchParams{
+			SearchType: 0, Query: keyword,
+			PageNum: 1, NumPerPage: 40,
+
+			// static values
+			Grp: 1, RemotePlace: "sizer.newclient.song",
+		})
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[Search] rpc call: %w", err)
+	}
+
+	respData := searchResponse{}
+	if err := json.Unmarshal(resp, &respData); err != nil {
+		return nil, fmt.Errorf("qqMusicClient[Search] unmarshal response: %w", err)
+	}
+
+	return respData.Body.Song.List, nil
+
+}

algo/qmc/client/track.go

@@ -0,0 +1,178 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/samber/lo"
+)
+
+type getTrackInfoParams struct {
+	Ctx   int   `json:"ctx"`
+	Ids   []int `json:"ids"`
+	Types []int `json:"types"`
+}
+
+type getTrackInfoResponse struct {
+	Tracks []*TrackInfo `json:"tracks"`
+}
+
+func (c *QQMusic) GetTracksInfo(ctx context.Context, songIDs []int) ([]*TrackInfo, error) {
+	resp, err := c.rpcCall(ctx,
+		"Protocol_UpdateSongInfo",
+		"CgiGetTrackInfo",
+		"music.trackInfo.UniformRuleCtrl",
+		&getTrackInfoParams{Ctx: 0, Ids: songIDs, Types: []int{0}},
+	)
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[GetTrackInfo] rpc call: %w", err)
+	}
+	respData := getTrackInfoResponse{}
+	if err := json.Unmarshal(resp, &respData); err != nil {
+		return nil, fmt.Errorf("qqMusicClient[GetTrackInfo] unmarshal response: %w", err)
+	}
+
+	return respData.Tracks, nil
+}
+
+func (c *QQMusic) GetTrackInfo(ctx context.Context, songID int) (*TrackInfo, error) {
+	tracks, err := c.GetTracksInfo(ctx, []int{songID})
+	if err != nil {
+		return nil, fmt.Errorf("qqMusicClient[GetTrackInfo] get tracks info: %w", err)
+	}
+
+	if len(tracks) == 0 {
+		return nil, fmt.Errorf("qqMusicClient[GetTrackInfo] track not found")
+	}
+
+	return tracks[0], nil
+}
+
+type TrackSinger struct {
+	Id    int    `json:"id"`
+	Mid   string `json:"mid"`
+	Name  string `json:"name"`
+	Title string `json:"title"`
+	Type  int    `json:"type"`
+	Uin   int    `json:"uin"`
+	Pmid  string `json:"pmid"`
+}
+type TrackAlbum struct {
+	Id       int    `json:"id"`
+	Mid      string `json:"mid"`
+	Name     string `json:"name"`
+	Title    string `json:"title"`
+	Subtitle string `json:"subtitle"`
+	Pmid     string `json:"pmid"`
+}
+type TrackInfo struct {
+	Id       int           `json:"id"`
+	Type     int           `json:"type"`
+	Mid      string        `json:"mid"`
+	Name     string        `json:"name"`
+	Title    string        `json:"title"`
+	Subtitle string        `json:"subtitle"`
+	Singer   []TrackSinger `json:"singer"`
+	Album    TrackAlbum    `json:"album"`
+	Mv       struct {
+		Id    int    `json:"id"`
+		Vid   string `json:"vid"`
+		Name  string `json:"name"`
+		Title string `json:"title"`
+		Vt    int    `json:"vt"`
+	} `json:"mv"`
+	Interval   int    `json:"interval"`
+	Isonly     int    `json:"isonly"`
+	Language   int    `json:"language"`
+	Genre      int    `json:"genre"`
+	IndexCd    int    `json:"index_cd"`
+	IndexAlbum int    `json:"index_album"`
+	TimePublic string `json:"time_public"`
+	Status     int    `json:"status"`
+	Fnote      int    `json:"fnote"`
+	File       struct {
+		MediaMid      string        `json:"media_mid"`
+		Size24Aac     int           `json:"size_24aac"`
+		Size48Aac     int           `json:"size_48aac"`
+		Size96Aac     int           `json:"size_96aac"`
+		Size192Ogg    int           `json:"size_192ogg"`
+		Size192Aac    int           `json:"size_192aac"`
+		Size128Mp3    int           `json:"size_128mp3"`
+		Size320Mp3    int           `json:"size_320mp3"`
+		SizeApe       int           `json:"size_ape"`
+		SizeFlac      int           `json:"size_flac"`
+		SizeDts       int           `json:"size_dts"`
+		SizeTry       int           `json:"size_try"`
+		TryBegin      int           `json:"try_begin"`
+		TryEnd        int           `json:"try_end"`
+		Url           string        `json:"url"`
+		SizeHires     int           `json:"size_hires"`
+		HiresSample   int           `json:"hires_sample"`
+		HiresBitdepth int           `json:"hires_bitdepth"`
+		B30S          int           `json:"b_30s"`
+		E30S          int           `json:"e_30s"`
+		Size96Ogg     int           `json:"size_96ogg"`
+		Size360Ra     []interface{} `json:"size_360ra"`
+		SizeDolby     int           `json:"size_dolby"`
+		SizeNew       []interface{} `json:"size_new"`
+	} `json:"file"`
+	Pay struct {
+		PayMonth   int `json:"pay_month"`
+		PriceTrack int `json:"price_track"`
+		PriceAlbum int `json:"price_album"`
+		PayPlay    int `json:"pay_play"`
+		PayDown    int `json:"pay_down"`
+		PayStatus  int `json:"pay_status"`
+		TimeFree   int `json:"time_free"`
+	} `json:"pay"`
+	Action struct {
+		Switch   int `json:"switch"`
+		Msgid    int `json:"msgid"`
+		Alert    int `json:"alert"`
+		Icons    int `json:"icons"`
+		Msgshare int `json:"msgshare"`
+		Msgfav   int `json:"msgfav"`
+		Msgdown  int `json:"msgdown"`
+		Msgpay   int `json:"msgpay"`
+		Switch2  int `json:"switch2"`
+		Icon2    int `json:"icon2"`
+	} `json:"action"`
+	Ksong struct {
+		Id  int    `json:"id"`
+		Mid string `json:"mid"`
+	} `json:"ksong"`
+	Volume struct {
+		Gain float64 `json:"gain"`
+		Peak float64 `json:"peak"`
+		Lra  float64 `json:"lra"`
+	} `json:"volume"`
+	Label       string   `json:"label"`
+	Url         string   `json:"url"`
+	Ppurl       string   `json:"ppurl"`
+	Bpm         int      `json:"bpm"`
+	Version     int      `json:"version"`
+	Trace       string   `json:"trace"`
+	DataType    int      `json:"data_type"`
+	ModifyStamp int      `json:"modify_stamp"`
+	Aid         int      `json:"aid"`
+	Tid         int      `json:"tid"`
+	Ov          int      `json:"ov"`
+	Sa          int      `json:"sa"`
+	Es          string   `json:"es"`
+	Vs          []string `json:"vs"`
+}
+
+func (t *TrackInfo) GetArtists() []string {
+	return lo.Map(t.Singer, func(v TrackSinger, i int) string {
+		return v.Name
+	})
+}
+
+func (t *TrackInfo) GetTitle() string {
+	return t.Title
+}
+
+func (t *TrackInfo) GetAlbum() string {
+	return t.Album.Name
+}

algo/qmc/qmc.go

@@ -27,9 +27,19 @@ type Decoder struct {
 	decodedKey []byte // decodedKey is the decoded key for cipher
 	cipher     common.StreamDecoder
 
-	rawMetaExtra1 int
+	songID        int
 	rawMetaExtra2 int
 
+	albumID      int
+	albumMediaID string
+
+	// cache
+	meta          common.AudioMeta
+	cover         []byte
+	embeddedCover bool          // embeddedCover is true if the cover is embedded in the file
+	probeBuf      *bytes.Buffer // probeBuf is the buffer for sniffing metadata, TODO: consider pipe?
+
+	// provider
 	logger *zap.Logger
 }
 
@@ -40,6 +50,8 @@ func (d *Decoder) Read(p []byte) (int, error) {
 	if n > 0 {
 		d.cipher.Decrypt(p[:n], d.offset)
 		d.offset += n
+
+		_, _ = d.probeBuf.Write(p[:n]) // bytes.Buffer.Write never return error
 	}
 	return n, err
 }
@@ -81,6 +93,9 @@ func (d *Decoder) Validate() error {
 	}
 	d.audio = io.LimitReader(d.raw, int64(d.audioLen))
 
+	// prepare for sniffing metadata
+	d.probeBuf = bytes.NewBuffer(make([]byte, 0, d.audioLen))
+
 	return nil
 }
 
@@ -199,7 +214,7 @@ func (d *Decoder) readRawMetaQTag() error {
 		return err
 	}
 
-	d.rawMetaExtra1, err = strconv.Atoi(items[1])
+	d.songID, err = strconv.Atoi(items[1])
 	if err != nil {
 		return err
 	}

algo/qmc/qmc_meta.go

@@ -0,0 +1,128 @@
+package qmc
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/samber/lo"
+
+	"unlock-music.dev/cli/algo/common"
+	"unlock-music.dev/cli/algo/qmc/client"
+	"unlock-music.dev/cli/internal/ffmpeg"
+)
+
+func (d *Decoder) GetAudioMeta(ctx context.Context) (common.AudioMeta, error) {
+	if d.meta != nil {
+		return d.meta, nil
+	}
+
+	if d.songID != 0 {
+		if err := d.getMetaBySongID(ctx); err != nil {
+			return nil, err
+		}
+		return d.meta, nil
+	}
+
+	embedMeta, err := ffmpeg.ProbeReader(ctx, d.probeBuf)
+	if err != nil {
+		return nil, fmt.Errorf("qmc[GetAudioMeta] probe reader: %w", err)
+	}
+	d.meta = embedMeta
+	d.embeddedCover = embedMeta.HasAttachedPic()
+
+	if !d.embeddedCover && embedMeta.HasMetadata() {
+		if err := d.searchMetaOnline(ctx, embedMeta); err != nil {
+			return nil, err
+		}
+		return d.meta, nil
+	}
+
+	return d.meta, nil
+}
+
+func (d *Decoder) getMetaBySongID(ctx context.Context) error {
+	c := client.NewQQMusicClient() // todo: use global client
+	trackInfo, err := c.GetTrackInfo(ctx, d.songID)
+	if err != nil {
+		return fmt.Errorf("qmc[GetAudioMeta] get track info: %w", err)
+	}
+
+	d.meta = trackInfo
+	d.albumID = trackInfo.Album.Id
+	if trackInfo.Album.Pmid == "" {
+		d.albumMediaID = trackInfo.Album.Pmid
+	} else {
+		d.albumMediaID = trackInfo.Album.Mid
+	}
+	return nil
+}
+
+func (d *Decoder) searchMetaOnline(ctx context.Context, original common.AudioMeta) error {
+	c := client.NewQQMusicClient() // todo: use global client
+	keyword := lo.WithoutEmpty(append(
+		[]string{original.GetTitle(), original.GetAlbum()},
+		original.GetArtists()...),
+	)
+	if len(keyword) == 0 {
+		return errors.New("qmc[searchMetaOnline] no keyword")
+	}
+
+	trackList, err := c.Search(ctx, strings.Join(keyword, " "))
+	if err != nil {
+		return fmt.Errorf("qmc[searchMetaOnline] search: %w", err)
+	}
+
+	if len(trackList) == 0 {
+		return errors.New("qmc[searchMetaOnline] no result")
+	}
+
+	meta := trackList[0]
+	d.meta = meta
+	d.albumID = meta.Album.Id
+	if meta.Album.Pmid == "" {
+		d.albumMediaID = meta.Album.Pmid
+	} else {
+		d.albumMediaID = meta.Album.Mid
+	}
+
+	return nil
+}
+
+func (d *Decoder) GetCoverImage(ctx context.Context) ([]byte, error) {
+	if d.cover != nil {
+		return d.cover, nil
+	}
+
+	if d.embeddedCover {
+		img, err := ffmpeg.ExtractAlbumArt(ctx, d.probeBuf)
+		if err != nil {
+			return nil, fmt.Errorf("qmc[GetCoverImage] extract album art: %w", err)
+		}
+
+		d.cover = img.Bytes()
+
+		return d.cover, nil
+	}
+
+	c := client.NewQQMusicClient() // todo: use global client
+	var err error
+
+	if d.albumMediaID != "" {
+		d.cover, err = c.AlbumCoverByMediaID(ctx, d.albumMediaID)
+		if err != nil {
+			return nil, fmt.Errorf("qmc[GetCoverImage] get cover by media id: %w", err)
+		}
+	} else if d.albumID != 0 {
+		d.cover, err = c.AlbumCoverByID(ctx, d.albumID)
+		if err != nil {
+			return nil, fmt.Errorf("qmc[GetCoverImage] get cover by id: %w", err)
+		}
+	} else {
+		return nil, errors.New("qmc[GetAudioMeta] album (or media) id is empty")
+	}
+
+	return d.cover, nil
+
+}

cmd/um/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -24,8 +25,10 @@ import (
 	_ "unlock-music.dev/cli/algo/tm"
 	_ "unlock-music.dev/cli/algo/xiami"
 	_ "unlock-music.dev/cli/algo/ximalaya"
+	"unlock-music.dev/cli/internal/ffmpeg"
 	"unlock-music.dev/cli/internal/logging"
 	"unlock-music.dev/cli/internal/sniff"
+	"unlock-music.dev/cli/internal/utils"
 )
 
 var AppVersion = "v0.0.6"
@@ -47,7 +50,9 @@ func main() {
 			&cli.StringFlag{Name: "output", Aliases: []string{"o"}, Usage: "path to output dir", Required: false},
 			&cli.BoolFlag{Name: "remove-source", Aliases: []string{"rs"}, Usage: "remove source file", Required: false, Value: false},
 			&cli.BoolFlag{Name: "skip-noop", Aliases: []string{"n"}, Usage: "skip noop decoder", Required: false, Value: true},
-			&cli.BoolFlag{Name: "supported-ext", Usage: "Show supported file extensions and exit", Required: false, Value: false},
+			&cli.BoolFlag{Name: "update-metadata", Usage: "update metadata & album art from network", Required: false, Value: false},
+
+			&cli.BoolFlag{Name: "supported-ext", Usage: "show supported file extensions and exit", Required: false, Value: false},
 		},
 
 		Action:          appMain,
@@ -102,9 +107,6 @@ func appMain(c *cli.Context) (err error) {
 		}
 	}
 
-	skipNoop := c.Bool("skip-noop")
-	removeSource := c.Bool("remove-source")
-
 	inputStat, err := os.Stat(input)
 	if err != nil {
 		return err
@@ -122,18 +124,30 @@ func appMain(c *cli.Context) (err error) {
 		return errors.New("output should be a writable directory")
 	}
 
-	if inputStat.IsDir() {
-		return dealDirectory(input, output, skipNoop, removeSource)
-	} else {
-		allDec := common.GetDecoder(inputStat.Name(), skipNoop)
-		if len(allDec) == 0 {
-			logger.Fatal("skipping while no suitable decoder")
+	proc := &processor{
+		outputDir:       output,
+		skipNoopDecoder: c.Bool("skip-noop"),
+		removeSource:    c.Bool("remove-source"),
+		updateMetadata:  c.Bool("update-metadata"),
 	}
-		return tryDecFile(input, output, allDec, removeSource)
+
+	if inputStat.IsDir() {
+		return proc.processDir(input)
+	} else {
+		return proc.processFile(input)
 	}
 
 }
-func dealDirectory(inputDir string, outputDir string, skipNoop bool, removeSource bool) error {
+
+type processor struct {
+	outputDir string
+
+	skipNoopDecoder bool
+	removeSource    bool
+	updateMetadata  bool
+}
+
+func (p *processor) processDir(inputDir string) error {
 	items, err := os.ReadDir(inputDir)
 	if err != nil {
 		return err
@@ -142,14 +156,9 @@ func dealDirectory(inputDir string, outputDir string, skipNoop bool, removeSourc
 		if item.IsDir() {
 			continue
 		}
-		allDec := common.GetDecoder(item.Name(), skipNoop)
-		if len(allDec) == 0 {
-			logger.Info("skipping while no suitable decoder", zap.String("file", item.Name()))
-			continue
-		}
 
 		filePath := filepath.Join(inputDir, item.Name())
-		err := tryDecFile(filePath, outputDir, allDec, removeSource)
+		err := p.processFile(filePath)
 		if err != nil {
 			logger.Error("conversion failed", zap.String("source", filePath), zap.Error(err))
 		}
@@ -157,18 +166,27 @@ func dealDirectory(inputDir string, outputDir string, skipNoop bool, removeSourc
 	return nil
 }
 
-func tryDecFile(inputFile string, outputDir string, allDec []common.NewDecoderFunc, removeSource bool) error {
+func (p *processor) processFile(filePath string) error {
+	allDec := common.GetDecoder(filePath, p.skipNoopDecoder)
+	if len(allDec) == 0 {
+		logger.Fatal("skipping while no suitable decoder")
+	}
+	return p.process(filePath, allDec)
+}
+
+func (p *processor) process(inputFile string, allDec []common.NewDecoderFunc) error {
 	file, err := os.Open(inputFile)
 	if err != nil {
 		return err
 	}
 	defer file.Close()
+	logger := logger.With(zap.String("source", inputFile))
 
 	decParams := &common.DecoderParams{
 		Reader:    file,
 		Extension: filepath.Ext(inputFile),
 		FilePath:  inputFile,
-		Logger:    logger.With(zap.String("source", inputFile)),
+		Logger:    logger,
 	}
 
 	var dec common.Decoder
@@ -185,31 +203,87 @@ func tryDecFile(inputFile string, outputDir string, allDec []common.NewDecoderFu
 		return errors.New("no any decoder can resolve the file")
 	}
 
+	params := &ffmpeg.UpdateMetadataParams{}
+
 	header := bytes.NewBuffer(nil)
 	_, err = io.CopyN(header, dec, 64)
 	if err != nil {
 		return fmt.Errorf("read header failed: %w", err)
 	}
+	audio := io.MultiReader(header, dec)
+	params.AudioExt = sniff.AudioExtensionWithFallback(header.Bytes(), ".mp3")
+
+	if p.updateMetadata {
+		if audioMetaGetter, ok := dec.(common.AudioMetaGetter); ok {
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+
+			// since ffmpeg doesn't support multiple input streams,
+			// we need to write the audio to a temp file.
+			// since qmc decoder doesn't support seeking & relying on ffmpeg probe, we need to read the whole file.
+			// TODO: support seeking or using pipe for qmc decoder.
+			params.Audio, err = utils.WriteTempFile(audio, params.AudioExt)
+			if err != nil {
+				return fmt.Errorf("updateAudioMeta write temp file: %w", err)
+			}
+			defer os.Remove(params.Audio)
+
+			params.Meta, err = audioMetaGetter.GetAudioMeta(ctx)
+			if err != nil {
+				logger.Warn("get audio meta failed", zap.Error(err))
+			}
+
+			if params.Meta == nil { // reset audio meta if failed
+				audio, err = os.Open(params.Audio)
+				if err != nil {
+					return fmt.Errorf("updateAudioMeta open temp file: %w", err)
+				}
+			}
+		}
+	}
+
+	if p.updateMetadata && params.Meta != nil {
+		if coverGetter, ok := dec.(common.CoverImageGetter); ok {
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+
+			if cover, err := coverGetter.GetCoverImage(ctx); err != nil {
+				logger.Warn("get cover image failed", zap.Error(err))
+			} else if imgExt, ok := sniff.ImageExtension(cover); !ok {
+				logger.Warn("sniff cover image type failed", zap.Error(err))
+			} else {
+				params.AlbumArtExt = imgExt
+				params.AlbumArt = cover
+			}
+		}
+	}
 
-	outExt := sniff.AudioExtensionWithFallback(header.Bytes(), ".mp3")
 	inFilename := strings.TrimSuffix(filepath.Base(inputFile), filepath.Ext(inputFile))
+	outPath := filepath.Join(p.outputDir, inFilename+params.AudioExt)
 
-	outPath := filepath.Join(outputDir, inFilename+outExt)
+	if params.Meta == nil {
 		outFile, err := os.OpenFile(outPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
 		if err != nil {
 			return err
 		}
 		defer outFile.Close()
 
-	if _, err := io.Copy(outFile, header); err != nil {
+		if _, err := io.Copy(outFile, audio); err != nil {
 			return err
 		}
-	if _, err := io.Copy(outFile, dec); err != nil {
+		outFile.Close()
+
+	} else {
+		ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+		defer cancel()
+
+		if err := ffmpeg.UpdateMeta(ctx, outPath, params); err != nil {
 			return err
 		}
+	}
 
 	// if source file need to be removed
-	if removeSource {
+	if p.removeSource {
 		err := os.RemoveAll(inputFile)
 		if err != nil {
 			return err

go.mod

@@ -3,11 +3,14 @@ module unlock-music.dev/cli
 go 1.19
 
 require (
+	github.com/go-flac/flacpicture v0.2.0
+	github.com/go-flac/flacvorbis v0.1.0
+	github.com/go-flac/go-flac v0.3.1
 	github.com/samber/lo v1.36.0
 	github.com/urfave/cli/v2 v2.23.6
 	go.uber.org/zap v1.24.0
 	golang.org/x/crypto v0.3.0
-	golang.org/x/exp v0.0.0-20221204150635-6dcec336b2bb
+	golang.org/x/exp v0.0.0-20221205204356-47842c84f3db
 	golang.org/x/text v0.5.0
 	unlock-music.dev/mmkv v0.0.0-20221204231432-41a75bd29939
 )

go.sum

@@ -4,9 +4,18 @@ github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46t
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/ddliu/go-httpclient v0.5.1 h1:ys4KozrhBaGdI1yuWIFwNNILqhnMU9ozTvRNfCTorvs=
+github.com/ddliu/go-httpclient v0.5.1/go.mod h1:8QVbjq00YK2f2MQyiKuWMdaKOFRcoD9VuubkNCNOuZo=
+github.com/go-flac/flacpicture v0.2.0 h1:rS/ZOR/ZxlEwMf3yOPFcTAmGyoV6rDtcYdd+6CwWQAw=
+github.com/go-flac/flacpicture v0.2.0/go.mod h1:M4a1J0v6B5NHsck4GA1yZg0vFQzETVPd3kuj6Ow+q9o=
+github.com/go-flac/flacvorbis v0.1.0 h1:xStJfPrZ/IoA2oBUEwgrlaSf+Opo6/YuQfkqVhkP0cM=
+github.com/go-flac/flacvorbis v0.1.0/go.mod h1:70N9vVkQ4Jew0oBWkwqDMIE21h7pMUtQJpnMD0js6XY=
+github.com/go-flac/go-flac v0.3.1 h1:BWA7HdO67S4ZLWSVHCxsDHuedFFu5RiV/wmuhvO6Hxo=
+github.com/go-flac/go-flac v0.3.1/go.mod h1:jG9IumOfAXr+7J40x0AiQIbJzXf9Y7+Zs/2CNWe4LMk=
 github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
 github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
 github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.8 h1:e6P7q2lk1O+qJJb4BtCQXlK8vWEO8V1ZeuEdJNOqZyg=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
@@ -35,8 +44,8 @@ go.uber.org/zap v1.24.0 h1:FiJd5l1UOLj0wCgbSE0rwwXHzEdAZS6hiiSnxJN/D60=
 go.uber.org/zap v1.24.0/go.mod h1:2kMP+WWQ8aoFoedH3T2sq6iJ2yDWpHbP0f6MQbS9Gkg=
 golang.org/x/crypto v0.3.0 h1:a06MkbcxBrEFc0w0QIZWXrH/9cCX6KJyWbBOIwAn+7A=
 golang.org/x/crypto v0.3.0/go.mod h1:hebNnKkNXi2UzZN1eVRvBB7co0a+JxK6XbPiWVs/3J4=
-golang.org/x/exp v0.0.0-20221204150635-6dcec336b2bb h1:QIsP/NmClBICkqnJ4rSIhnrGiGR7Yv9ZORGGnmmLTPk=
-golang.org/x/exp v0.0.0-20221204150635-6dcec336b2bb/go.mod h1:CxIveKay+FTh1D0yPZemJVgC/95VzuuOLq5Qi4xnoYc=
+golang.org/x/exp v0.0.0-20221205204356-47842c84f3db h1:D/cFflL63o2KSLJIwjlcIt8PR064j/xsmdEJL/YvY/o=
+golang.org/x/exp v0.0.0-20221205204356-47842c84f3db/go.mod h1:CxIveKay+FTh1D0yPZemJVgC/95VzuuOLq5Qi4xnoYc=
 golang.org/x/text v0.5.0 h1:OLmvp0KP+FVG99Ct/qFiL/Fhk4zp4QQnZ7b2U+5piUM=
 golang.org/x/text v0.5.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

internal/ffmpeg/ffmpeg.go

@@ -0,0 +1,125 @@
+package ffmpeg
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+
+	"unlock-music.dev/cli/algo/common"
+	"unlock-music.dev/cli/internal/utils"
+)
+
+func ExtractAlbumArt(ctx context.Context, rd io.Reader) (*bytes.Buffer, error) {
+	cmd := exec.CommandContext(ctx, "ffmpeg",
+		"-i", "pipe:0", // input from stdin
+		"-an",              // disable audio
+		"-codec:v", "copy", // copy video(image) codec
+		"-f", "image2", // use image2 muxer
+		"pipe:1", // output to stdout
+	)
+
+	cmd.Stdin = rd
+	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
+	cmd.Stdout, cmd.Stderr = stdout, stderr
+
+	if err := cmd.Run(); err != nil {
+		return nil, fmt.Errorf("ffmpeg run: %w", err)
+	}
+
+	return stdout, nil
+}
+
+type UpdateMetadataParams struct {
+	Audio    string // required
+	AudioExt string // required
+
+	Meta common.AudioMeta // required
+
+	AlbumArt    []byte // optional
+	AlbumArtExt string // required if AlbumArt is not nil
+}
+
+func UpdateMeta(ctx context.Context, outPath string, params *UpdateMetadataParams) error {
+	if params.AudioExt == ".flac" {
+		return updateMetaFlac(ctx, outPath, params)
+	} else {
+		return updateMetaFFmpeg(ctx, outPath, params)
+	}
+}
+func updateMetaFFmpeg(ctx context.Context, outPath string, params *UpdateMetadataParams) error {
+	builder := newFFmpegBuilder()
+
+	out := newOutputBuilder(outPath) // output to file
+	builder.SetFlag("y")             // overwrite output file
+	builder.AddOutput(out)
+
+	// input audio -> output audio
+	builder.AddInput(newInputBuilder(params.Audio)) // input 0: audio
+	out.AddOption("map", "0:a")
+	out.AddOption("codec:a", "copy")
+
+	// input cover -> output cover
+	if params.AlbumArt != nil &&
+		params.AudioExt != ".wav" /* wav doesn't support attached image */ {
+
+		// write cover to temp file
+		artPath, err := utils.WriteTempFile(bytes.NewReader(params.AlbumArt), params.AlbumArtExt)
+		if err != nil {
+			return fmt.Errorf("updateAudioMeta write temp file: %w", err)
+		}
+		defer os.Remove(artPath)
+
+		builder.AddInput(newInputBuilder(artPath)) // input 1: cover
+		out.AddOption("map", "1:v")
+
+		switch params.AudioExt {
+		case ".ogg": // ogg only supports theora codec
+			out.AddOption("codec:v", "libtheora")
+		case ".m4a": // .m4a(mp4) requires set codec, disposition, stream metadata
+			out.AddOption("codec:v", "mjpeg")
+			out.AddOption("disposition:v", "attached_pic")
+			out.AddMetadata("s:v", "title", "Album cover")
+			out.AddMetadata("s:v", "comment", "Cover (front)")
+		case ".mp3":
+			out.AddOption("codec:v", "mjpeg")
+			out.AddMetadata("s:v", "title", "Album cover")
+			out.AddMetadata("s:v", "comment", "Cover (front)")
+		default: // other formats use default behavior
+		}
+	}
+
+	// set file metadata
+	album := params.Meta.GetAlbum()
+	if album != "" {
+		out.AddMetadata("", "album", album)
+	}
+
+	title := params.Meta.GetTitle()
+	if album != "" {
+		out.AddMetadata("", "title", title)
+	}
+
+	artists := params.Meta.GetArtists()
+	if len(artists) != 0 {
+		// TODO: it seems that ffmpeg doesn't support multiple artists
+		out.AddMetadata("", "artist", strings.Join(artists, " / "))
+	}
+
+	if params.AudioExt == ".mp3" {
+		out.AddOption("write_id3v1", "true")
+		out.AddOption("id3v2_version", "3")
+	}
+
+	// execute ffmpeg
+	cmd := builder.Command(ctx)
+
+	if stdout, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("ffmpeg run: %w, %s", err, string(stdout))
+	}
+
+	return nil
+}

internal/ffmpeg/ffprobe.go

@@ -0,0 +1,141 @@
+package ffmpeg
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"os/exec"
+	"strings"
+
+	"github.com/samber/lo"
+)
+
+type Result struct {
+	Format  *Format   `json:"format"`
+	Streams []*Stream `json:"streams"`
+}
+
+func (r *Result) HasAttachedPic() bool {
+	return lo.ContainsBy(r.Streams, func(s *Stream) bool {
+		return s.CodecType == "video"
+	})
+}
+
+func (r *Result) getTagByKey(key string) string {
+	for k, v := range r.Format.Tags {
+		if key == strings.ToLower(k) {
+			return v
+		}
+	}
+
+	for _, stream := range r.Streams { // try to find in streams
+		if stream.CodecType != "audio" {
+			continue
+		}
+		for k, v := range stream.Tags {
+			if key == strings.ToLower(k) {
+				return v
+			}
+		}
+	}
+	return ""
+}
+func (r *Result) GetTitle() string {
+	return r.getTagByKey("title")
+}
+
+func (r *Result) GetAlbum() string {
+	return r.getTagByKey("album")
+}
+
+func (r *Result) GetArtists() []string {
+	artists := strings.Split(r.getTagByKey("artist"), "/")
+	for i := range artists {
+		artists[i] = strings.TrimSpace(artists[i])
+	}
+	return artists
+}
+
+func (r *Result) HasMetadata() bool {
+	return r.GetTitle() != "" || r.GetAlbum() != "" || len(r.GetArtists()) > 0
+}
+
+type Format struct {
+	Filename       string            `json:"filename"`
+	NbStreams      int               `json:"nb_streams"`
+	NbPrograms     int               `json:"nb_programs"`
+	FormatName     string            `json:"format_name"`
+	FormatLongName string            `json:"format_long_name"`
+	StartTime      string            `json:"start_time"`
+	Duration       string            `json:"duration"`
+	BitRate        string            `json:"bit_rate"`
+	ProbeScore     int               `json:"probe_score"`
+	Tags           map[string]string `json:"tags"`
+}
+
+type Stream struct {
+	Index          int               `json:"index"`
+	CodecName      string            `json:"codec_name"`
+	CodecLongName  string            `json:"codec_long_name"`
+	CodecType      string            `json:"codec_type"`
+	CodecTagString string            `json:"codec_tag_string"`
+	CodecTag       string            `json:"codec_tag"`
+	SampleFmt      string            `json:"sample_fmt"`
+	SampleRate     string            `json:"sample_rate"`
+	Channels       int               `json:"channels"`
+	ChannelLayout  string            `json:"channel_layout"`
+	BitsPerSample  int               `json:"bits_per_sample"`
+	RFrameRate     string            `json:"r_frame_rate"`
+	AvgFrameRate   string            `json:"avg_frame_rate"`
+	TimeBase       string            `json:"time_base"`
+	StartPts       int               `json:"start_pts"`
+	StartTime      string            `json:"start_time"`
+	BitRate        string            `json:"bit_rate"`
+	Disposition    *ProbeDisposition `json:"disposition"`
+	Tags           map[string]string `json:"tags"`
+}
+
+type ProbeDisposition struct {
+	Default         int `json:"default"`
+	Dub             int `json:"dub"`
+	Original        int `json:"original"`
+	Comment         int `json:"comment"`
+	Lyrics          int `json:"lyrics"`
+	Karaoke         int `json:"karaoke"`
+	Forced          int `json:"forced"`
+	HearingImpaired int `json:"hearing_impaired"`
+	VisualImpaired  int `json:"visual_impaired"`
+	CleanEffects    int `json:"clean_effects"`
+	AttachedPic     int `json:"attached_pic"`
+	TimedThumbnails int `json:"timed_thumbnails"`
+	Captions        int `json:"captions"`
+	Descriptions    int `json:"descriptions"`
+	Metadata        int `json:"metadata"`
+	Dependent       int `json:"dependent"`
+	StillImage      int `json:"still_image"`
+}
+
+func ProbeReader(ctx context.Context, rd io.Reader) (*Result, error) {
+	cmd := exec.CommandContext(ctx, "ffprobe",
+		"-v", "quiet", // disable logging
+		"-print_format", "json", // use json format
+		"-show_format", "-show_streams", "-show_error", // retrieve format and streams
+		"pipe:0", // input from stdin
+	)
+
+	cmd.Stdin = rd
+	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
+	cmd.Stdout, cmd.Stderr = stdout, stderr
+
+	if err := cmd.Run(); err != nil {
+		return nil, err
+	}
+
+	ret := new(Result)
+	if err := json.Unmarshal(stdout.Bytes(), ret); err != nil {
+		return nil, err
+	}
+
+	return ret, nil
+}

internal/ffmpeg/meta_flac.go

@@ -0,0 +1,90 @@
+package ffmpeg
+
+import (
+	"context"
+	"mime"
+	"strings"
+
+	"github.com/go-flac/flacpicture"
+	"github.com/go-flac/flacvorbis"
+	"github.com/go-flac/go-flac"
+	"golang.org/x/exp/slices"
+)
+
+func updateMetaFlac(_ context.Context, outPath string, m *UpdateMetadataParams) error {
+	f, err := flac.ParseFile(m.Audio)
+	if err != nil {
+		return err
+	}
+
+	// generate comment block
+	comment := flacvorbis.MetaDataBlockVorbisComment{Vendor: "unlock-music.dev"}
+
+	// add metadata
+	title := m.Meta.GetTitle()
+	if title != "" {
+		_ = comment.Add(flacvorbis.FIELD_TITLE, title)
+	}
+
+	album := m.Meta.GetAlbum()
+	if album != "" {
+		_ = comment.Add(flacvorbis.FIELD_ALBUM, album)
+	}
+
+	artists := m.Meta.GetArtists()
+	for _, artist := range artists {
+		_ = comment.Add(flacvorbis.FIELD_ARTIST, artist)
+	}
+
+	existCommentIdx := slices.IndexFunc(f.Meta, func(b *flac.MetaDataBlock) bool {
+		return b.Type == flac.VorbisComment
+	})
+	if existCommentIdx >= 0 { // copy existing comment fields
+		exist, err := flacvorbis.ParseFromMetaDataBlock(*f.Meta[existCommentIdx])
+		if err != nil {
+			for _, s := range exist.Comments {
+				if strings.HasPrefix(s, flacvorbis.FIELD_TITLE+"=") && title != "" ||
+					strings.HasPrefix(s, flacvorbis.FIELD_ALBUM+"=") && album != "" ||
+					strings.HasPrefix(s, flacvorbis.FIELD_ARTIST+"=") && len(artists) != 0 {
+					continue
+				}
+				comment.Comments = append(comment.Comments, s)
+			}
+		}
+	}
+
+	// add / replace flac comment
+	cmtBlock := comment.Marshal()
+	if existCommentIdx < 0 {
+		f.Meta = append(f.Meta, &cmtBlock)
+	} else {
+		f.Meta[existCommentIdx] = &cmtBlock
+	}
+
+	if m.AlbumArt != nil {
+
+		cover, err := flacpicture.NewFromImageData(
+			flacpicture.PictureTypeFrontCover,
+			"Front cover",
+			m.AlbumArt,
+			mime.TypeByExtension(m.AlbumArtExt),
+		)
+		if err != nil {
+			return err
+		}
+		coverBlock := cover.Marshal()
+		f.Meta = append(f.Meta, &coverBlock)
+
+		// add / replace flac cover
+		coverIdx := slices.IndexFunc(f.Meta, func(b *flac.MetaDataBlock) bool {
+			return b.Type == flac.Picture
+		})
+		if coverIdx < 0 {
+			f.Meta = append(f.Meta, &coverBlock)
+		} else {
+			f.Meta[coverIdx] = &coverBlock
+		}
+	}
+
+	return f.Save(outPath)
+}

internal/ffmpeg/options.go

@@ -0,0 +1,131 @@
+package ffmpeg
+
+import (
+	"context"
+	"os/exec"
+	"strings"
+)
+
+type ffmpegBuilder struct {
+	binary  string            // ffmpeg binary path
+	options map[string]string // global options
+	inputs  []*inputBuilder   // input options
+	outputs []*outputBuilder  // output options
+}
+
+func newFFmpegBuilder() *ffmpegBuilder {
+	return &ffmpegBuilder{
+		binary:  "ffmpeg",
+		options: make(map[string]string),
+	}
+}
+
+func (b *ffmpegBuilder) AddInput(src *inputBuilder) {
+	b.inputs = append(b.inputs, src)
+}
+
+func (b *ffmpegBuilder) AddOutput(dst *outputBuilder) {
+	b.outputs = append(b.outputs, dst)
+}
+
+func (b *ffmpegBuilder) SetBinary(bin string) {
+	b.binary = bin
+}
+
+func (b *ffmpegBuilder) SetFlag(flag string) {
+	b.options[flag] = ""
+}
+
+func (b *ffmpegBuilder) SetOption(name, value string) {
+	b.options[name] = value
+}
+
+func (b *ffmpegBuilder) Args() (args []string) {
+	for name, val := range b.options {
+		args = append(args, "-"+name)
+		if val != "" {
+			args = append(args, val)
+		}
+	}
+
+	for _, input := range b.inputs {
+		args = append(args, input.Args()...)
+	}
+	for _, output := range b.outputs {
+		args = append(args, output.Args()...)
+	}
+
+	return
+}
+
+func (b *ffmpegBuilder) Command(ctx context.Context) *exec.Cmd {
+	bin := "ffmpeg"
+	if b.binary != "" {
+		bin = b.binary
+	}
+
+	return exec.CommandContext(ctx, bin, b.Args()...)
+}
+
+// inputBuilder is the builder for ffmpeg input options
+type inputBuilder struct {
+	path    string
+	options map[string][]string
+}
+
+func newInputBuilder(path string) *inputBuilder {
+	return &inputBuilder{
+		path:    path,
+		options: make(map[string][]string),
+	}
+}
+
+func (b *inputBuilder) AddOption(name, value string) {
+	b.options[name] = append(b.options[name], value)
+}
+
+func (b *inputBuilder) Args() (args []string) {
+	for name, values := range b.options {
+		for _, val := range values {
+			args = append(args, "-"+name, val)
+		}
+	}
+	return append(args, "-i", b.path)
+}
+
+// outputBuilder is the builder for ffmpeg output options
+type outputBuilder struct {
+	path    string
+	options map[string][]string
+}
+
+func newOutputBuilder(path string) *outputBuilder {
+	return &outputBuilder{
+		path:    path,
+		options: make(map[string][]string),
+	}
+}
+
+func (b *outputBuilder) AddOption(name, value string) {
+	b.options[name] = append(b.options[name], value)
+}
+
+func (b *outputBuilder) Args() (args []string) {
+	for name, values := range b.options {
+		for _, val := range values {
+			args = append(args, "-"+name, val)
+		}
+	}
+	return append(args, b.path)
+}
+
+// AddMetadata is the shortcut for adding "metadata" option
+func (b *outputBuilder) AddMetadata(stream, key, value string) {
+	optVal := strings.TrimSpace(key) + "=" + strings.TrimSpace(value)
+
+	if stream != "" {
+		b.AddOption("metadata:"+stream, optVal)
+	} else {
+		b.AddOption("metadata", optVal)
+	}
+}

internal/sniff/audio.go

@@ -13,7 +13,7 @@ type Sniffer interface {
 
 var audioExtensions = map[string]Sniffer{
 	// ref: https://mimesniff.spec.whatwg.org
-	".mp3": prefixSniffer("ID3"),
+	".mp3": prefixSniffer("ID3"), // todo: check mp3 without ID3v2 tag
 	".ogg": prefixSniffer("OggS"),
 	".wav": prefixSniffer("RIFF"),
 

internal/sniff/image.go

@@ -0,0 +1,30 @@
+package sniff
+
+// ref: https://mimesniff.spec.whatwg.org
+var imageMIMEs = map[string]Sniffer{
+	"image/jpeg": prefixSniffer{0xFF, 0xD8, 0xFF},
+	"image/png":  prefixSniffer{'P', 'N', 'G', '\r', '\n', 0x1A, '\n'},
+	"image/bmp":  prefixSniffer("BM"),
+	"image/webp": prefixSniffer("RIFF"),
+	"image/gif":  prefixSniffer("GIF8"),
+}
+
+// ImageMIME sniffs the well-known image types, and returns its MIME.
+func ImageMIME(header []byte) (string, bool) {
+	for ext, sniffer := range imageMIMEs {
+		if sniffer.Sniff(header) {
+			return ext, true
+		}
+	}
+	return "", false
+}
+
+// ImageExtension is equivalent to ImageMIME, but returns file extension
+func ImageExtension(header []byte) (string, bool) {
+	ext, ok := ImageMIME(header)
+	if !ok {
+		return "", false
+	}
+	// todo: use mime.ExtensionsByType
+	return "." + ext[6:], true // "image/" is 6 bytes
+}

internal/utils/temp.go

@@ -0,0 +1,24 @@
+package utils
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+func WriteTempFile(rd io.Reader, ext string) (string, error) {
+	audioFile, err := os.CreateTemp("", "*"+ext)
+	if err != nil {
+		return "", fmt.Errorf("ffmpeg create temp file: %w", err)
+	}
+
+	if _, err := io.Copy(audioFile, rd); err != nil {
+		return "", fmt.Errorf("ffmpeg write temp file: %w", err)
+	}
+
+	if err := audioFile.Close(); err != nil {
+		return "", fmt.Errorf("ffmpeg close temp file: %w", err)
+	}
+
+	return audioFile.Name(), nil
+}