Hi,
I’m writing a C++ program to validate the integrity of a Fragmented MP4 file
containing AAC audio.
This program would parse the FMP4 file, read each audio packet, attachment ADTS
headers, and then try to decode the AAC using libfdk_aac.
I am using libavformat, and I am able to parse the MP4 atoms correctly, however
I’m having issues figuring out the best way to attach the ADTS headers.
My current idea is to use a libavformat mp4 demuxed and send that to an adts
muxer. I’ve written all the code to do it now; but I’m now getting errors like
so:
[adts @ 0x7fae51001600] MPEG-4 AOT 0 is not allowed in ADTS
I’m not sure what to do now.
My code is as below:
AudioAssetReader::AudioAssetReader(const AudioAssetReaderInput &input) throw
(invalid_argument):
input(input),
segmentsIter(input.getBeginSegmentsIter()), audioBufferSize(409600),
adtsPacketBufferSize(409600) {
if (input.getSegments()->empty()) {
throw invalid_argument("A reader must read at least 1 segment
of audio!");
}
this->audioBuffer = new uint8_t[audioBufferSize];
// create the main context used to parse the audio asset, segment by
segment
bool isBufferWritable = false;
this->assetSegmentReaderContext = avio_alloc_context(this->audioBuffer,
this->audioBufferSize, isBufferWritable, this, AudioAssetReader::readSegment,
NULL, NULL);
this->assetParsingContext = avformat_alloc_context();
this->assetParsingContext->pb = this->assetSegmentReaderContext;
this->assetParsingContext->flags = AVFMT_FLAG_CUSTOM_IO;
// create another context used to append ADTS headers to the parsed
segments, if we need them
this->initializeADTSMuxerContext(input);
}
void AudioAssetReader::initializeADTSMuxerContext(const AudioAssetReaderInput
&input) {
this->adtsPacketBuffer = new uint8_t[adtsPacketBufferSize];
this->adtsPacket = av_packet_alloc();
// create another context used to append ADTS headers to the parsed
segments, if we need them
bool isBufferWritable = true;
avformat_alloc_output_context2(&this->adtsMuxerContext, NULL, "adts",
NULL);
this->adtsMuxerWriterContext =
avio_alloc_context(this->adtsPacketBuffer, this->adtsPacketBufferSize,
isBufferWritable, this, NULL, AudioAssetReader::writeADTSPacket, NULL);
this->adtsMuxerContext->pb = this->adtsMuxerWriterContext;
// initialize an ADTS stream
AVCodecID aacCodec = AVCodecID::AV_CODEC_ID_AAC;
AVCodec *codec = avcodec_find_encoder(aacCodec);
AVStream *stream = avformat_new_stream(this->adtsMuxerContext, codec);
stream->id = this->adtsMuxerContext->nb_streams - 1;
stream->time_base.den = input.getSampleRateHz();
stream->time_base.num = 1;
// configure the stream with the details of the AAC packets
AVCodecParameters *codecParameters = stream->codecpar;
codecParameters->codec_id = aacCodec;
codecParameters->bit_rate = input.getBitrateBps();
codecParameters->profile =
this->getAACProfileForCodec(input.getCodec());
codecParameters->sample_rate = input.getSampleRateHz();
codecParameters->channels = input.getChannelCount();
codecParameters->codec_type = AVMEDIA_TYPE_AUDIO;
codecParameters->channel_layout =
av_get_default_channel_layout(input.getChannelCount());
uint8_t* header = new uint8_t[7];
memset(header, 1, 7);
//header[3] = 2 << 6;
codecParameters->extradata = header;
codecParameters->extradata_size = 7;
// write out a header to the muxer; this is a no-op for our purposes
const int result = avformat_write_header(this->adtsMuxerContext, NULL);
if (result < 0) {
char *message = new char[AV_ERROR_MAX_STRING_SIZE];
av_make_error_string(message, AV_ERROR_MAX_STRING_SIZE, result);
cerr<<endl<<"Failed to write the ADTS muxer header due to:
"<<result<<": "<<message<<endl;
delete[] message;
}
}
Ronak_______________________________________________
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