h264 ffmpeg: How to initialize ffmpeg to decode NALs created with x264

问题

I have encoded some frames using x264, using x264_encoder_encode and after that I have created AVPackets using a function like this:

bool PacketizeNals( uint8_t* a_pNalBuffer, int a_nNalBufferSize, AVPacket* a_pPacket )
{
    if ( !a_pPacket )
return false;
    a_pPacket->data = a_pNalBuffer;
    a_pPacket->size = a_nNalBufferSize;
    a_pPacket->stream_index = 0;
    a_pPacket->flags = AV_PKT_FLAG_KEY;

    a_pPacket->pts = int64_t(0x8000000000000000);
    a_pPacket->dts = int64_t(0x8000000000000000);
}

I call this function like this:

x264_nal_t* nals;
int num_nals = encode_frame(pic, &nals);
for (int i = 0; i < num_nals; i++)
{
    AVPacket* pPacket = ( AVPacket* )av_malloc( sizeof( AVPacket ) );
    av_init_packet( pPacket );
    if ( PacketizeNals( nals[i].p_payload, nals[i].i_payload, pPacket ) )
    {
        packets.push_back( pPacket );
    }
}

Now what I want to do is to decode these AVPackets using avcodec_decode_video2. I think the problem is that I haven't initialized properly the decoder because to encode I used "ultrafast" profile and "zerolatency" tune ( x264 ) and to decode I don't know how to specify to ffmpeg these options. In some examples I have read people initialize the decoder using the file where the video is stored, but in this case I have directly the AVPackets. What I'm doing to try to decode is:

avcodec_init();  
avcodec_register_all();  
AVCodec* pCodec;  
pCodec=avcodec_find_decoder(CODEC_ID_H264);  
AVCodecContext* pCodecContext;  
pCodecContext=avcodec_alloc_context();  
avcodec_open(pCodecContext,pCodec);  
pCodecContext->width = 320;
pCodecContext->height = 200;
pCodecContext->extradata = NULL;
unsigned int nNumPackets = packets.size();
int frameFinished = 0;
for ( auto it = packets.begin(); it != packets.end(); it++ )
{
    AVFrame* pFrame;
    pFrame = avcodec_alloc_frame();
    AVPacket* pPacket = *it;
    int iReturn = avcodec_decode_video2( pCodecContext, pFrame, &frameFinished, pPacket );
}

But in iReturn always is -1.

Can anyone help me? Sorry if my knowledge in this area es low, I'm new.

Thanks.

回答1:

I have written a simple client/server application that streams raw RGB video using lib x264 for encoding and ffmpeg for decoding. You can find the code here: https://github.com/filippobrizzi/raw_rgb_straming

It shows how to setup x264 and ffmpeg to encode/decode.

回答2:

Right now you initialize the decoder like

pCodecContext->extradata = NULL;

this is not correct. You need to allocate a memory for this field and copy data from the encoder's AVCodecContext::extradata into the allocated buffer. AVCodecContext::extradata_size specifies size of this extradata buffer in bytes

回答3:

Make sure that you are building correct packets. See how this is done in the ffmpeg: http://ffmpeg.org/doxygen/trunk/libx264_8c_source.html (static int encode_nals(AVCodecContext *ctx, AVPacket *pkt, x264_nal_t *nals, int nnal) and static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame, int *got_packet))

来源：https://stackoverflow.com/questions/14322670/h264-ffmpeg-how-to-initialize-ffmpeg-to-decode-nals-created-with-x264

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c++

ffmpeg

decode

h.264

x264