FFMpeg How to use multithreading? - multithreading

Question

I want to decode H264 by ffmpeg, BUT finally I found the decode function only used one cpu core
system monitor
env: Ubuntu 14.04 FFMpeg 3.2.4 CPU i7-7500U
So, I search ffmpeg multithreading and decide using all cpu cores for decoding.
I set AVCodecContext as this:
//Init works
//codecId=AV_CODEC_ID_H264;
avcodec_register_all();
pCodec = avcodec_find_decoder(codecId);
if (!pCodec)
{
printf("Codec not found\n");
return -1;
}
pCodecCtx = avcodec_alloc_context3(pCodec);
if (!pCodecCtx)
{
printf("Could not allocate video codec context\n");
return -1;
}
pCodecParserCtx=av_parser_init(codecId);
if (!pCodecParserCtx)
{
printf("Could not allocate video parser context\n");
return -1;
}
pCodecCtx->thread_count = 4;
pCodecCtx->thread_type = FF_THREAD_FRAME;
pCodec->capabilities &= CODEC_CAP_TRUNCATED;
pCodecCtx->flags |= CODEC_FLAG_TRUNCATED;
if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
{
printf("Could not open codec\n");
return -1;
}
av_log_set_level(AV_LOG_QUIET);
av_init_packet(&packet);
//parse and decode
//after av_parser_parse2, the packet has a complete frame data
//in decode function, I just call avcodec_decode_video2 and do some frame copy work
while (cur_size>0)
{
int len = av_parser_parse2(
pCodecParserCtx, pCodecCtx,
&packet.data, &packet.size,
cur_ptr, cur_size,
AV_NOPTS_VALUE, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
cur_ptr += len;
cur_size -= len;
if(GetPacketSize()==0)
continue;
AVFrame *pFrame = av_frame_alloc();
int ret = Decode(pFrame);
if (ret < 0)
{
continue;
}
if (ret)
{
//some works
}
}
But nothing different with before.
How can I use multithreading in FFMpeg? Any advise?

Answer 1

pCodec->capabilities &= CODEC_CAP_TRUNCATED;
And that's your bug. Please remove this line. The return value of avcodec_find_decoder() should for all practical intents and purposes be considered const.
Specifically, this statement removes the AV_CODEC_CAP_FRAME_THREADS flag from the codec's capabilities, thus effectively disabling frame-multithreading in the rest of the code.