[FFmpeg-user] ffmpeg libx264 VBR and CBR output generates different POC, possible bug

[Maxim Levkov]

Hi Roger and Carl,

Needless to say, after countless hours of tinkering, I have solved the
problem, at least I see a consistently equal output from both CBR and VBR,
as far as the POC ( picture order count ) goes.

To help gather consistency, I've added a 2 pass and stats file to my
command line. Then, I use stats file as source for rest of my bitrate
variations and sequences.

If you go through my post, earlier email, and use the sources for
reproduction, then you can see the change. At least I've been able to
reproduce the case consistently with bad and good results.

Here is a modified command line that solved my case:

Here is my command line for the CBR and VBR outputs:

/* CBR: */
-------
b:\ffmpeg.exe -v 9 -loglevel 99 -i "F:\700_scale(640x360)_1min.
avi" -threads 0 ^ -force_key_frames
00:00:29.946,00:00:44.961,00:01:17.368,00:01:32.383 ^ -c:v libx264
-sws_flags lanczos -cmp rd ^
-x264opts
pass=1:stats=1:bitrate=700:vbv_maxrate=700:vbv_bufsize=700:nal_hrd=cbr:rc_lookahead=40:interlaced=0:scenecut=0:cabac=1:keyint=120:level=3.2:deblock=1,0,0:aud=1:qpmin=16:qpmax=51:qpstep=10:ref=2:mixed-refs=1:subme=9:me=esa:chroma_me=0:merange=64:8x8dct=0:fast_pskip=0:chroma_qp_offset=0:trellis=2:psy=0:bframes=0:weightp=2:slices=0:sliced_threads=0:ipratio=1.40:qcomp=0.60:partitions=p8x8,b8x8,i8x8,i4x4:direct=auto:mbtree=0:colorprim=bt709:transfer=bt709:colormatrix=bt709
^
-aspect 16:9  -pix_fmt yuv420p -c:a libvo_aacenc -ab 128000 -ar 44100 -ac 2
-f mp4 -y "b:\forced_i_frames_700_640x360_700_5secGOP_CBR_1min_POCtest.mp4"
-vstats_file b:\consoleOutput_POC_CBR_vstats.txt
2>b:\consoleOutput_POC_CBR-loglevel99.txt

/* CBR: */
-------
b:\ffmpeg.exe -v 9 -loglevel 99 -i "F:\700_scale(640x360)_1min.
avi" -threads 0 ^ -force_key_frames
00:00:29.946,00:00:44.961,00:01:17.368,00:01:32.383 ^ -c:v libx264
-sws_flags lanczos -cmp rd ^
-x264opts
pass=2:stats=1:bitrate=700:vbv_maxrate=700:vbv_bufsize=700:nal_hrd=cbr:rc_lookahead=40:interlaced=0:scenecut=0:cabac=1:keyint=120:level=3.2:deblock=1,0,0:aud=1:qpmin=16:qpmax=51:qpstep=10:ref=2:mixed-refs=1:subme=9:me=esa:chroma_me=0:merange=64:8x8dct=0:fast_pskip=0:chroma_qp_offset=0:trellis=2:psy=0:bframes=0:weightp=2:slices=0:sliced_threads=0:ipratio=1.40:qcomp=0.60:partitions=p8x8,b8x8,i8x8,i4x4:direct=auto:mbtree=0:colorprim=bt709:transfer=bt709:colormatrix=bt709
^
-aspect 16:9  -pix_fmt yuv420p -c:a libvo_aacenc -ab 128000 -ar 44100 -ac 2
-f mp4 -y "b:\forced_i_frames_700_640x360_700_5secGOP_CBR_1min_POCtest.mp4"
-vstats_file b:\consoleOutput_POC_CBR_vstats.txt
2>b:\consoleOutput_POC_CBR-loglevel99.txt
-------
/* VBR */
-------
b:\ffmpeg.exe -v 9 -loglevel 99 -i "F:\700_scale(640x360)-1min.avi"
-threads 0 ^ -force_key_frames
00:00:29.946,00:00:44.961,00:01:17.368,00:01:32.383 ^ -c:v libx264
-sws_flags lanczos -cmp rd ^
-x264opts
pass=2:stats=1:bitrate=700:vbv_maxrate=750:vbv_bufsize=800:nal_hrd=vbr:rc_lookahead=40:interlaced=0:scenecut=0:cabac=1:keyint=120:level=3.2:deblock=1,0,0:aud=1:qpmin=16:qpmax=51:qpstep=10:ref=2:mixed-refs=1:subme=9:me=esa:chroma_me=0:merange=64:8x8dct=0:fast_pskip=0:chroma_qp_offset=0:trellis=2:psy=0:bframes=0:weightp=2:slices=0:sliced_threads=0:ipratio=1.40:qcomp=0.60:partitions=p8x8,b8x8,i8x8,i4x4:direct=auto:mbtree=0:colorprim=bt709:transfer=bt709:colormatrix=bt709
^
-aspect 16:9  -pix_fmt yuv420p -c:a libvo_aacenc -ab 128000 -ar 44100 -ac 2
-f mp4 -y
"b:\forced_i_frames_700_640x360_800_5secGOP_VBR_1min_POCtest.mp4"
-vstats_file b:\consoleOutput_POC_VBR_vstats.txt
2>b:\consoleOutput_POC_VBR-loglevel99.txt
----------------------------------------

Note the change "-x264opts pass=2:stats=1:..... " for both VBR and CBR.

Where, 'stats=1', '1' is just a temp extensionless name of the file that
holds the first pass statistics. I've tried to use FFMPEG indirect '-pass
1' and '-pass 2'  options, not within -x264opts, and the result was not
consistent and rather unsuccessful. Once I placed it within the 'x264opts',
the output result was consistent, even "log" files looked differently from
the FFMPEG '-pass 1'/'-pass 2' option.

So, at this moment, I'm not sure whether it needs to be considered a bug,
or something else, but results speak for themselves.

Regards,
Maxim






On Mon, Nov 12, 2012 at 10:54 PM, Maxim Levkov <maxim.levkov at gmail.com>wrote:

> Hi Roger,
>
> No, not yet. This was on my list, next.
>
> Will update in short order.
>
> Regards,
> Maxim
>
>
>
> On Mon, Nov 12, 2012 at 9:04 PM, Roger Pack <rogerdpack2 at gmail.com> wrote:
>
>> > area of POC (picture order count). Hence, I'm not sure if this is an
>> issue
>> > that derives from FFMPEG or libx264, it might be the latter, but could
>> be
>> > the FFMPEG '-force_key_frames' option. I think POC should be the same
>> for
>> > CBR and VBR.
>>
>> Have you tried it with the "x264" executable?
>> _______________________________________________
>> ffmpeg-user mailing list
>> ffmpeg-user at ffmpeg.org
>> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
>>
>
>