[x264-devel] output at crf 20 larger than source??

[sean darcy]

I'm trying to transcode a clip taken by a Canon HD camcorder:

ffprobe -i Act1a-2011.08.20_20-27-08.m2t
ffprobe version N-32125-g24ddfb2, Copyright (c) 2007-2011 the FFmpeg developers
........
Input #0, mpegts, from 'Act1a-2011.08.20_20-27-08.m2t':
  Duration: 00:00:00.46, start: 0.937767, bitrate: -2147483 kb/s
  Program 100
    Stream #0.0[0x810]: Video: mpeg2video (Main) ([2][0][0][0] /
0x0002), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], 25000 kb/s, 29.97 fps,
29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0.1[0x814]: Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz,
stereo, s16, 384 kb/s

The source has 76265 frames.

I used this command:

 mplayer -nosound -benchmark -vo yuv4mpeg:file=>(x264 --demuxer y4m
--crf 20 --threads auto --preset veryslow --tune film--output
act1a.264) Act1a-2011.08.20_20-27-08.m2t


I didn't let it finish. After 68800 frames the output was larger than the input:

8589584076 Sep  1 21:27 Act1a-2011.08.20_20-27-08.m2t
9775037726 Sep 11 09:37 act1a.264

Here's the x264 stats:

mplayer -nosound -benchmark -vo yuv4mpeg:file=>(x264 --demuxer y4m
--crf 20 --preset veryslow --tune film --threads auto --output
act1a.264 - ) Act1a-2011.08.20_20-27-08.m2t
x264 [info]: frame I:278   Avg QP:22.10  size:270356
x264 [info]: frame P:11461 Avg QP:24.70  size:184179
x264 [info]: frame B:57081 Avg QP:26.08  size:132951
x264 [info]: consecutive B-frames:  0.5%  0.2%  0.5%  6.6% 12.3% 46.9%
17.0% 14.1%  2.0%
x264 [info]: mb I  I16..4:  0.4% 97.8%  1.8%
x264 [info]: mb P  I16..4:  0.1% 61.0%  0.6%  P16..4: 19.6% 15.4%
2.7%  0.6%  0.1%    skip: 0.0%
x264 [info]: mb B  I16..4:  0.0% 24.9%  0.1%  B16..8: 33.6% 19.1%
6.5%  direct:12.5%  skip: 3.4%  L0:46.5% L1:31.8% BI:21.7%
x264 [info]: 8x8 transform intra:99.4% inter:86.6%
x264 [info]: direct mvs  spatial:100.0% temporal:0.0%
x264 [info]: coded y,uvDC,uvAC intra: 99.4% 69.9% 16.2% inter: 81.6% 47.1% 2.9%
x264 [info]: i16 v,h,dc,p: 26% 20% 25% 29%
x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 14%  6% 24%  8%  8% 11%  8% 12% 10%
x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 15% 25%  7%  6%  8% 10%  9%  9% 11%
x264 [info]: i8c dc,h,v,p: 25% 34% 30% 11%
x264 [info]: Weighted P-Frames: Y:16.1% UV:5.9%
x264 [info]: ref P L0: 27.5% 11.1% 16.3%  8.4%  7.0%  5.0%  4.7%  3.0%
 3.0%  2.4%  2.5%  2.0%  2.0%  1.8%  1.9%  1.4%
x264 [info]: ref B L0: 58.4% 13.0%  6.7%  4.0%  3.2%  2.9%  2.5%  1.7%
 1.5%  1.4%  1.3%  1.3%  1.2%  0.7%  0.2%
x264 [info]: ref B L1: 89.4% 10.6%
x264 [info]: kb/s:34055.00

aborted at input frame 68897, output frame 68820
encoded 68820 frames, 1.26 fps, 34055.00 kb/s

So it's gone from 25000 kb/s to 34055.00 kb/s! What's going wrong?

sean