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106 lines
3.7 KiB
Go
106 lines
3.7 KiB
Go
package mpeg
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// https://github.com/mstorsjo/fdk-aac/blob/f285813ec15e7c6f8e4839c9eb4f6b0cd2da1990/libMpegTPEnc/src/tpenc_asc.cpp
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// https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/wp/FraunhoferIIS_Application-Bulletin_AAC-Transport-Formats.pdf
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// https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/aac_adtstoasc_bsf.c
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import (
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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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"github.com/wader/fq/pkg/scalar"
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)
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var aacFrameFormat decode.Group
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func init() {
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registry.MustRegister(decode.Format{
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Name: format.ADTS_FRAME,
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Description: "Audio Data Transport Stream frame",
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DecodeFn: adtsFrameDecoder,
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Dependencies: []decode.Dependency{
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{Names: []string{format.AAC_FRAME}, Group: &aacFrameFormat},
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},
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})
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}
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var protectionAbsentNames = scalar.BoolToDescription{
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true: "No CRC",
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false: "Has CRC",
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}
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func adtsFrameDecoder(d *decode.D, in interface{}) interface{} {
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/*
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adts_frame() {
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adts_fixed_header();
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adts_variable_header();
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if (number_of_raw_data_blocks_in_frame == 0) {
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adts_error_check();
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raw_data_block();
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} else {
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adts_header_error_check();
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for( i = 0; i <= number_of_raw_data_blocks_in_frame; i++ ) {
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raw_data_block();
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adts_raw_data_block_error_check();
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}
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}
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}
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*/
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// A 12 syncword 0xFFF, all bits must be 1
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// B 1 MPEG Version: 0 for MPEG-4, 1 for MPEG-2
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// C 2 Layer: always 0
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// D 1 protection absent, Warning, set to 1 if there is no CRC and 0 if there is CRC
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// E 2 profile, the MPEG-4 Audio Object Type minus 1
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// F 4 MPEG-4 Sampling Frequency Index (15 is forbidden)
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// G 1 private bit, guaranteed never to be used by MPEG, set to 0 when encoding, ignore when decoding
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// H 3 MPEG-4 Channel Configuration (in the case of 0, the channel configuration is sent via an inband PCE)
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// I 1 originality, set to 0 when encoding, ignore when decoding
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// J 1 home, set to 0 when encoding, ignore when decoding
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// K 1 copyrighted id bit, the next bit of a centrally registered copyright identifier, set to 0 when encoding, ignore when decoding
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// L 1 copyright id start, signals that this frame's copyright id bit is the first bit of the copyright id, set to 0 when encoding, ignore when decoding
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// M 13 frame length, this value must include 7 or 9 bytes of header length: FrameLength = (ProtectionAbsent == 1 ? 7 : 9) + size(AACFrame)
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// O 11 Buffer fullness
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// P 2 Number of AAC frames (RDBs) in ADTS frame minus 1, for maximum compatibility always use 1 AAC frame per ADTS frame
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// Q 16 CRC if protection absent is 0
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d.FieldU12("syncword", d.AssertU(0b1111_1111_1111), scalar.Bin)
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d.FieldU1("mpeg_version", scalar.UToSymStr{0: "mpeg4", 1: "mpeg2_aac"})
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d.FieldU2("layer", d.AssertU(0))
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protectionAbsent := d.FieldBool("protection_absent", protectionAbsentNames)
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objectType := d.FieldU2("profile", scalar.UAdd(1), format.MPEGAudioObjectTypeNames)
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d.FieldUFn("sampling_frequency", decodeEscapeValueAbsFn(4, 24, 0), frequencyIndexHzMap)
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d.FieldU1("private_bit")
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d.FieldU3("channel_configuration", channelConfigurationNames)
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d.FieldU1("originality")
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d.FieldU1("home")
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d.FieldU1("copyrighted")
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d.FieldU1("copyright")
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frameLength := d.FieldU13("frame_length")
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dataLength := int64(frameLength - 7)
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if !protectionAbsent {
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// TODO: multuple RDBs CRCs
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dataLength -= 2
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}
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d.FieldU11("buffer_fullness")
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numberOfRDBs := d.FieldU2("number_of_rdbs", scalar.UAdd(1))
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if !protectionAbsent {
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d.FieldU16("crc")
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}
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if dataLength < 0 {
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d.Fatalf("dataLength < 0")
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}
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d.FieldArray("raw_data_blocks", func(d *decode.D) {
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for i := uint64(0); i < numberOfRDBs; i++ {
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d.FieldFormatLen("raw_data_block", dataLength*8, aacFrameFormat, format.AACFrameIn{ObjectType: int(objectType)})
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}
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})
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return nil
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}
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