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https://github.com/wader/fq.git
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88 lines
2.2 KiB
Go
88 lines
2.2 KiB
Go
package mp3
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// https://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
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// http://gabriel.mp3-tech.org/mp3infotag.html
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// https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/mp3dec.c
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import (
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"github.com/wader/fq/format"
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"github.com/wader/fq/pkg/decode"
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"github.com/wader/fq/pkg/interp"
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)
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func init() {
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interp.RegisterFormat(
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format.MP3_Frame_XING,
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&decode.Format{
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Description: "MP3 frame Xing/Info tag",
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Groups: []*decode.Group{format.MP3_Frame_Tags},
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DecodeFn: mp3FrameTagXingDecode,
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})
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}
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func mp3FrameTagXingDecode(d *decode.D) any {
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d.FieldUTF8("header", 4, d.StrAssert("Xing", "Info"))
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lamePresent := false
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qualityPresent := false
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tocPresent := false
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bytesPresent := false
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framesPresent := false
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d.FieldStruct("present_flags", func(d *decode.D) {
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d.FieldU("unused", 27)
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lamePresent = d.FieldBool("lame")
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qualityPresent = d.FieldBool("quality")
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tocPresent = d.FieldBool("toc")
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bytesPresent = d.FieldBool("bytes")
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framesPresent = d.FieldBool("frames")
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})
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if framesPresent {
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d.FieldU32BE("frames")
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}
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if bytesPresent {
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d.FieldU32BE("bytes")
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}
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if tocPresent {
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d.FieldArray("toc", func(d *decode.D) {
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for i := 0; i < 100; i++ {
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d.FieldU8("entry")
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}
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})
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}
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if qualityPresent {
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d.FieldU32BE("quality")
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}
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// this is mix of what ffmpeg and mediainfo does to detect lame extensions
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peekLame, _ := d.TryPeekBytes(4)
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peekLaneStr := string(peekLame)
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hasLameHeader := (peekLaneStr == "LAME" ||
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peekLaneStr == "Lavf" ||
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peekLaneStr == "Lavc" ||
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peekLaneStr == "GOGO" ||
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peekLaneStr == "L3.9")
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if lamePresent || hasLameHeader {
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d.FieldUTF8("encoder", 9)
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d.FieldU4("tag_revision")
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d.FieldU4("vbr_method")
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d.FieldU8("lowpass_filter") // TODO: /100
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d.FieldU32("replay_gain_peak")
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d.FieldU16("radio_replay_gain")
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d.FieldU16("audiophile_replay_gain")
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d.FieldU4("lame_flags")
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d.FieldU4("lame_ath_type")
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d.FieldU8("abr_vbr") // TODO:
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d.FieldU12("encoder_delay") // TODO:
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d.FieldU12("encoder_padding") // TODO:
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d.FieldU8("misc") // TODO:
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d.FieldU8("mp3_gain") // TODO:
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d.FieldU16("preset") // TODO:
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d.FieldU32("length")
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d.FieldU16("music_crc") // TODO:
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d.FieldU16("tag_crc") // TODO:
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}
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return nil
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}
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