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124 lines
3.0 KiB
Go
124 lines
3.0 KiB
Go
package mp3
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// TODO: vbri
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import (
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"fmt"
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"github.com/wader/fq/format"
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"github.com/wader/fq/format/registry"
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"github.com/wader/fq/pkg/decode"
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)
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var headerFormat decode.Group
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var footerFormat decode.Group
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var mp3Frame decode.Group
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// TODO: format options default
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const maxUniqueHeaderConfigs = 5
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const maxSyncSeek = 64 * 1024 * 8
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func init() {
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registry.MustRegister(decode.Format{
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Name: format.MP3,
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ProbeOrder: 20, // after most others (silent samples and jpeg header can look like mp3 sync)
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Description: "MP3 file",
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Groups: []string{format.PROBE},
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DecodeFn: mp3Decode,
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Dependencies: []decode.Dependency{
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{Names: []string{format.ID3V2}, Group: &headerFormat},
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{
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Names: []string{
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format.ID3V1,
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format.ID3V11,
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format.APEV2,
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},
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Group: &footerFormat,
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},
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{Names: []string{format.MP3_FRAME}, Group: &mp3Frame},
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},
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})
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}
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func mp3Decode(d *decode.D, in interface{}) interface{} {
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// things in a mp3 stream usually have few unique combinations of.
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// does not include bitrate on purpose
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type headerConfig struct {
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MPEGVersion int
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ProtectionAbsent bool
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SampleRate int
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ChannelsIndex int
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ChannelModeIndex int
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}
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uniqueHeaderConfigs := map[headerConfig]struct{}{}
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// there are mp3s files in the wild with multiple headers, two id3v2 tags etc
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d.FieldArray("headers", func(d *decode.D) {
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for d.NotEnd() {
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if dv, _, _ := d.FieldTryFormat("header", headerFormat, nil); dv == nil {
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return
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}
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}
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})
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lastValidEnd := int64(0)
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validFrames := 0
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decodeFailures := 0
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d.FieldArray("frames", func(d *decode.D) {
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for d.NotEnd() {
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syncLen, _, err := d.TryPeekFind(16, 8, maxSyncSeek, func(v uint64) bool {
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return (v&0b1111_1111_1110_0000 == 0b1111_1111_1110_0000 && // sync header
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v&0b0000_0000_0001_1000 != 0b0000_0000_0000_1000 && // not reserved mpeg version
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v&0b0000_0000_0000_0110 == 0b0000_0000_0000_0010) // layer 3
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})
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if err != nil || syncLen < 0 {
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break
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}
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if syncLen > 0 {
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d.SeekRel(syncLen)
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}
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dv, v, _ := d.FieldTryFormat("frame", mp3Frame, nil)
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if dv == nil {
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decodeFailures++
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d.SeekRel(8)
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continue
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}
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mfo, ok := v.(format.MP3FrameOut)
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if !ok {
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panic(fmt.Sprintf("expected MP3FrameOut got %#+v", v))
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}
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uniqueHeaderConfigs[headerConfig{
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MPEGVersion: mfo.MPEGVersion,
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ProtectionAbsent: mfo.ProtectionAbsent,
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SampleRate: mfo.SampleRate,
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ChannelsIndex: mfo.ChannelsIndex,
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ChannelModeIndex: mfo.ChannelModeIndex,
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}] = struct{}{}
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lastValidEnd = d.Pos()
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validFrames++
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if len(uniqueHeaderConfigs) >= maxUniqueHeaderConfigs {
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d.Errorf("too many unique header configurations")
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}
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}
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})
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if validFrames == 0 || (validFrames < 2 && decodeFailures > 0) {
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d.Errorf("no frames found")
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}
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d.SeekAbs(lastValidEnd)
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d.FieldArray("footers", func(d *decode.D) {
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for d.NotEnd() {
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if dv, _, _ := d.FieldTryFormat("footer", footerFormat, nil); dv == nil {
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return
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}
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}
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})
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return nil
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}
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