[Libav-user] Decoding too slow (avcodec_send_packet() / avcodec_receive_frame())

[Danny Wilson]

I'm using ffmpeg libraries to decode, scale, and re-encode video within an MPEG transport stream. I've just recompiled from source to v3.3.2 and changed from the old avcodec_decode_video2() API to the new send/receive API.

Both the old and new APIs decode the video very slowly.

25 fps video = 1 frame every 40ms. However, I see 70 to 120ms per frame to decode. This is a file translator so need it to run faster than real time.

The code outline is below. Anyone have any ideas on how to improve the decoding speed? There are other posts about the deprecated avcodec_decode_video2() being slow; none of those were resolved. The new API doesn't run any faster...

gettimeofday(&tv1, NULL);
int rc = av_read_frame(pFormatContext, pESPacket);
gettimeofday(&tv2, NULL);

int ret = avcodec_send_packet(pDecoderContext, pESPacket);
if (ret < 0)
    continue;

ret = avcodec_receive_frame(pDecoderContext, pFrameDec);
if (ret != 0)
{
    printf("avcodec_receive_frame error: %d\n", ret);
    continue;
}
gettimeofday(&tv3, 0);

u_long twoMinusOne   = (tv2.tv_sec - tv1.tv_sec) * 1000000 + tv2.tv_usec - tv1.tv_usec;
u_long threeMinusTwo = (tv3.tv_sec - tv2.tv_sec) * 1000000 + tv3.tv_usec - tv2.tv_usec;

size_t pktSize = mPacketQueue.getTsPktListSize();
printf("  DECODE ReadFrame %lu usec, DecodeVideo %lu usec. mTsPacketList %u items\n", twoMinusOne, threeMinusTwo, pktSize);

transcodeFrame(pFrameDec);

// Scale and re-encode //
-- call avscale to downsample
-- call avcodec_encode_video2() to encode
Some Output

DECODE ReadFrame 6 usec, DecodeVideo 154273 usec.
Dump mpFrameEnc with DateTime: 
  AVFrame Info frame 720 X 406. PTS = 305700353  PKT_PTS = 305700353 Linesize[0]=720. Linesize[1]=360. Linesize[2]=360.   
Time taken to ENCODE video frame = 3685 usec. Scaling time 4 usec

DECODE ReadFrame 8 usec, DecodeVideo 128203 usec.
Time taken to ENCODE video frame = 3724 usec. Scaling time 3 usec

DECODE ReadFrame 8 usec, DecodeVideo 69321 usec.
Time taken to ENCODE video frame = 3577 usec. Scaling time 3 usec
FFMPEG Version

Tests running on core2 duo 3.2 GHz, 32-bit Centos 6.

bin/ffmpeg
ffmpeg version 3.3.2 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-11)
  configuration: --prefix=/mnt/swdevel/DVStor/source_build/ext/ffmpeg-build --libdir=/mnt/swdevel/DVStor/source_build/ext/ffmpeg-build/lib3p_build --shlibdir=/mnt/swdevel/DVStor/source_build/ext/ffmpeg-build/lib3p_build --disable-static --enable-shared --disable-cuda --disable-cuvid --disable-nvenc --enable-libx264 --enable-gpl --extra-cflags=-I/usr/local/include/libx264
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Hyper fast Audio and Video encoder

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