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unlock-music-cli/internal/sniff/audio.go

62 lines
1.7 KiB
Go

package sniff
import "bytes"
type Sniffer interface {
Sniff(header []byte) bool
}
var audioExtensions = map[string]Sniffer{
// ref: https://mimesniff.spec.whatwg.org
".mp3": prefixSniffer("ID3"),
".ogg": prefixSniffer("OggS"),
".wav": prefixSniffer("RIFF"),
// ref: https://www.loc.gov/preservation/digital/formats/fdd/fdd000027.shtml
".wma": prefixSniffer{
0x30, 0x26, 0xb2, 0x75, 0x8e, 0x66, 0xcf, 0x11,
0xa6, 0xd9, 0x00, 0xaa, 0x00, 0x62, 0xce, 0x6c,
},
// ref: https://www.garykessler.net/library/file_sigs.html
".m4a": mpeg4Sniffer{}, // MPEG-4 container, m4a treat as audio
".aac": prefixSniffer{0xFF, 0xF1}, // MPEG-4 AAC-LC
".flac": prefixSniffer("fLaC"), // ref: https://xiph.org/flac/format.html
".dff": prefixSniffer("FRM8"), // DSDIFF, ref: https://www.sonicstudio.com/pdf/dsd/DSDIFF_1.5_Spec.pdf
}
// AudioExtension sniffs the known audio types, and returns the file extension.
// header is recommended to at least 16 bytes.
func AudioExtension(header []byte) (string, bool) {
for ext, sniffer := range audioExtensions {
if sniffer.Sniff(header) {
return ext, true
}
}
return "", false
}
// AudioExtensionWithFallback is equivalent to AudioExtension, but returns fallback
// most likely to use .mp3 as fallback, because mp3 files may not have ID3v2 tag.
func AudioExtensionWithFallback(header []byte, fallback string) string {
ext, ok := AudioExtension(header)
if !ok {
return fallback
}
return ext
}
type prefixSniffer []byte
func (s prefixSniffer) Sniff(header []byte) bool {
return bytes.HasPrefix(header, s)
}
type mpeg4Sniffer struct{}
func (mpeg4Sniffer) Sniff(header []byte) bool {
return len(header) >= 8 && bytes.Equal([]byte("ftyp"), header[4:8])
}