Alexey Khit
62 lines
2.1 KiB
Go
62 lines
2.1 KiB
Go
package aac
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import (
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"encoding/hex"
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"github.com/AlexxIT/go2rtc/pkg/bits"
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"github.com/AlexxIT/go2rtc/pkg/core"
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)
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func IsADTS(b []byte) bool {
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_ = b[1]
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return len(b) > 7 && b[0] == 0xFF && b[1]&0xF0 == 0xF0
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}
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func ADTSToCodec(b []byte) *core.Codec {
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// 1. Check ADTS header
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if !IsADTS(b) {
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return nil
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}
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// 2. Decode ADTS params
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// https://wiki.multimedia.cx/index.php/ADTS
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rd := bits.NewReader(b)
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_ = rd.ReadBits(12) // Syncword, all bits must be set to 1
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_ = rd.ReadBit() // MPEG Version, set to 0 for MPEG-4 and 1 for MPEG-2
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_ = rd.ReadBits(2) // Layer, always set to 0
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_ = rd.ReadBit() // Protection absence, set to 1 if there is no CRC and 0 if there is CRC
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objType := rd.ReadBits8(2) + 1 // Profile, the MPEG-4 Audio Object Type minus 1
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sampleRateIdx := rd.ReadBits8(4) // MPEG-4 Sampling Frequency Index
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_ = rd.ReadBit() // Private bit, guaranteed never to be used by MPEG, set to 0 when encoding, ignore when decoding
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channels := rd.ReadBits16(3) // MPEG-4 Channel Configuration
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//_ = rd.ReadBit() // Originality, set to 1 to signal originality of the audio and 0 otherwise
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//_ = rd.ReadBit() // Home, set to 1 to signal home usage of the audio and 0 otherwise
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//_ = rd.ReadBit() // Copyright ID bit
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//_ = rd.ReadBit() // Copyright ID start
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//_ = rd.ReadBits(13) // Frame length
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//_ = rd.ReadBits(11) // Buffer fullness
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//_ = rd.ReadBits(2) // Number of AAC frames (Raw Data Blocks) in ADTS frame minus 1
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//_ = rd.ReadBits(16) // CRC check
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// 3. Encode RTP config
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wr := bits.NewWriter(nil)
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wr.WriteBits8(objType, 5)
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wr.WriteBits8(sampleRateIdx, 4)
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wr.WriteBits16(channels, 4)
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conf := wr.Bytes()
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codec := &core.Codec{
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Name: core.CodecAAC,
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ClockRate: sampleRates[sampleRateIdx],
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Channels: channels,
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FmtpLine: fmtp + hex.EncodeToString(conf),
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}
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return codec
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}
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func ReadADTSSize(b []byte) uint16 {
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// AAAAAAAA AAAABCCD EEFFFFGH HHIJKLMM MMMMMMMM MMMOOOOO OOOOOOPP (QQQQQQQQ QQQQQQQQ)
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return uint16(b[3]&0x03)<<(8+3) | uint16(b[4])<<3 | uint16(b[5]>>5)
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}
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