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Missing frames when encoding 16x16 video to MPEG4/MPEG2/H264

Submitted by Vincent Penquerc'h @vincent

Link to original bug (#732631)

Description

+++ This bug was initially created as a clone of Bug 732351 +++

When encoding 16x16 video to MPEG, a sanity check triggers in ffmpeg, which causes frames to be not encoded.

To reproduce:

  1. Create a 16x16 h264 file:
    gst-launch-1.0 videotestsrc pattern=6 num-buffers=1000 ! \
    "video/x-raw, format=(string)I420, width=(int)16, height=(int)16, \
    framerate=(fraction)1/1" ! x264enc ! qtmux ! filesink location=/tmp/test.mov

  2. Play this file:
    gst-launch-1.0 playbin uri="file:///tmp/test.mov" video-sink=xvimagesink

  3. See grey output, instead of the solid blue (pattern 6) we expected.

Tracing shows the encoding earlies out in libav from a sanity check on size (which is apparently too strict):

gst-libs/ext/libav/libavcodec/mpegvideo_enc.c, function encode_thread:

        if(s->pb.buf_end - s->pb.buf - (put_bits_count(&s->pb)>>3) < MAX_MB_BYTES){  
            av_log(s->avctx, AV_LOG_ERROR, "encoded frame too large\n");  
            return -1;  
        }

Commenting out the return -1 above fixes the issue (albeit at the likely cost of possible buffer overflow).

Depends on