Hello,
I have a code in which I am receiving H264 sps, pps and frame packets
and want to mux them into matroska, using libav*.
As instructed in the sample codes, I am doing roughly the following:
AVFormatContext *oc;
AVCodec *codec;
AVCodecContext *ctx;
AVStream *stream;
AVPacket *avpkt;
avformat_alloc_output_context2(&oc, NULL, NULL, "output.mkv");
codec = avcodec_find_decoder(AV_CODEC_ID_H264); // AVCodec = possible
parameters for a codec
ctx = avcodec_alloc_context3(codec); // reserve memory for
codec related thingies.. AVCodecContext = defines codec parameters (as
per AVCodec)
stream = avformat_new_stream(oc,ctx->codec); // add new stream to
AVFormatContext ctx->codec is "AVCodec"
avcodec_copy_context(stream->codec,ctx); // stream.codec ==
AVCodecContext (we populate the codec parameters for stream "stream")
// THE QUESTION: How do we populate stream->codec, i.e. AVCodecContext
instance, correctly for the stream? (***)
avio_open(&oc->pb, filename, AVIO_FLAG_WRITE); // open the matroska
file ..
ret = avformat_write_header(oc, NULL);
...
av_interleaved_write_frame(oc,avpkt); // pass packets to the muxer
The problem is, that prior to opening the matroska file, stream->codec
has no information about picture dimensions (matroska header requires
pic dimensions).
I can solve this by passing sps, pps and an i-frame to a decoder (with
avcodec_decode_video2), which populates an AVCodecContext with correct
picture information, and then use that AVCodecContext.
However, this seems to be an overkill.. I do not want to decode
anything, just to get the codec parameters from sps and pps. Is there a
simpler way to achieve this?
In fact, for files (AVFormatContext), there is the routine
"avformat_find_stream_info" for such task. At the present case,
however, I only have raw sps, pps and frame packets.
One observation more: the sps, pps and I-frame (nal unit types 7,8 & 5),
must the aggregated into a single packet in order for the matroska muxer
to work.
Regards,
Sampsa
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