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

  19 février 2024, par Raul Calvo

  I encoded some frames using x264, using x264_encoder_encode() and after that I 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 properly initialized the decoder because to encode I used "ultrafast" profile and "zerolatency" tune (x264) and to decode I don't know how to specify these options to ffmpeg.

  


  In some examples I have read people initialize the decoder using the file where the video is stored, but in this case I have the AVPackets directly.

  


  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 iReturn is always -1.

  


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

  


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

  19 février 2024, par Raul Calvo

  I encoded some frames using x264, using x264_encoder_encode() and after that I 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 properly initialized the decoder because to encode I used "ultrafast" profile and "zerolatency" tune (x264) and to decode I don't know how to specify these options to ffmpeg.

  


  In some examples I have read people initialize the decoder using the file where the video is stored, but in this case I have the AVPackets directly.

  


  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 iReturn is always -1.

  


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

  


• Having ffmpeg add a repeating text overlay on a video

  30 mai 2020, par Caius Jard

  I'm looking to create an overlay that cycles through the characters in a string over and over. I've succeeded in using a sendcmd file to put A, B, C, D, E on the first 5 seconds of a video

  



  0  drawtext reinit 'text=A';
1  drawtext reinit 'text=B';
2  drawtext reinit 'text=C';
3  drawtext reinit 'text=D';
4  drawtext reinit 'text=E';


  



  But it doesn't cycle and I haven't been able to find a way to make it, because sendcmd looks like it just takes a simple timecode. I could make a command file 3600 lines long for my hour video, with those commands in over and over (the command file would be generated programmatically so not onerous)

  



  ---

  



  After some considerable experimenting I was able to do it with 5 separate drawtext :

  



  drawtext=fontfile=/Windows/Fonts/bauhs93.ttf:fontsize=1024:fontcolor=white@0.1:bordercolor=black@0.1:borderw=10:r=250:text='A':x=if(trunc(mod(t\,5))\,-2000\,(w-tw)/2),
drawtext=fontfile=/Windows/Fonts/bauhs93.ttf:fontsize=1024:fontcolor=white@0.1:bordercolor=black@0.1:borderw=10:r=250:text='B':x=if(trunc(mod(t\,5))-1\,-2000\,(w-tw)/2),
drawtext=fontfile=/Windows/Fonts/bauhs93.ttf:fontsize=1024:fontcolor=white@0.1:bordercolor=black@0.1:borderw=10:r=250:text='C':x=if(trunc(mod(t\,5))-2\,-2000\,(w-tw)/2),
drawtext=fontfile=/Windows/Fonts/bauhs93.ttf:fontsize=1024:fontcolor=white@0.1:bordercolor=black@0.1:borderw=10:r=250:text='D':x=if(trunc(mod(t\,5))-3\,-2000\,(w-tw)/2),
drawtext=fontfile=/Windows/Fonts/bauhs93.ttf:fontsize=1024:fontcolor=white@0.1:bordercolor=black@0.1:borderw=10:r=250:text='E':x=if(trunc(mod(t\,5))-4\,-2000\,(w-tw)/2)


  



  But as can be seen, I have to repeat a lot of stuff here. Is there any slicker way ? It does seem to have a noticeable effect on encoding speed the more chars are added

  



  I was hoping that text expressions would help but it seems I can only return numerics from the values, so this expression didn't work out :

  



  %{e:if(trunc(mod(t,5)),'A', '')%{e:if(trunc(mod(t,5))-1,'B', '') ...