[FFmpeg-devel] eval lavfi filter

[Víctor Paesa]

Hi,

Michael Niedermayer said:
> On Wed, Feb 25, 2009 at 01:04:15PM +0100, V?ctor Paesa wrote:
>> Hi,
>> Michael Niedermayer said:
>> > On Wed, Feb 25, 2009 at 09:07:57AM +0100, V?ctor Paesa wrote:
>> >> Hi,
>> >>
>> >> Michael Niedermayer said:
>> >> > On Tue, Feb 24, 2009 at 11:56:54PM +0100, Stefano Sabatini wrote:
>> >> >> On date Tuesday 2009-02-24 23:26:23 +0100, Michael Niedermayer
>> >> encoded:
>> >> >> > On Tue, Feb 24, 2009 at 10:39:22PM +0100, Stefano Sabatini
>> wrote:
>> >> >> > > Hi.
>> >> >> > >
>> >> >> > > On date Tuesday 2009-01-20 09:37:21 +0100, V?ctor Paesa
>> >> encoded:
>> >> >> > > > There is also a problem for filters that remove frames, as
>> >> >> ffmpeg uses/expects the fps of the input video (instead of the
>> >> filtered one) and generates duplicated frames to reach that.
>> >> >> >
>> >> >> > ffmpeg should not duplicate frames anymore if the container
>> can
>> >> >> handle it
>> >> >>
>> >> >> Could someone give some more hints about this?
>> >> >
>> >> > just try the example that caused frame duplication and check the
>> >> resulting file, avi/mov/mp4/nut should have no duplicate frames
>> anymore. feedback and bugreports welcome ...
>> >> >
>> >> >
>> >> >>
>> >> >> Also I suppose this is not necessarily a lavfi-related issue,
>> >> right?
>> >> >
>> >> > no
>> >>
>> >> Right, I was able to trace it (but not able to fix) to ffmpeg.c, it
>> seems that do_video() is duplicating frames. Maybe adding a new
>> "-vsync 3" that would not perfom any frame rate duplication?
>> >
>> > just tried
>> > ffmpeg -v 9 -i matrixbench_mpeg2.mpg -r 90 test.avi
>> >
>> > no duplicated frames are generated and considering you provide not a
>> single word of a hint of what you did or what did not work i cant
>> help
>>
>> I'm sorry, I answered without reading your commit 17555, please
>> discard my comments.
>>
>> Some tests on r17555:
>>
>> in.avi =
>> http://samples.mplayerhq.hu/avi/fpstest/gwl-bounce-sample-25fps.avi
>> that is 60 seconds long and has 1500 frames.
>>
>> $ ffmpeg  -i in.avi -vfilters fps=1 -y -an out_fps1.avi
>> FFmpeg version SVN-r17555, Copyright (c) 2000-2009 Fabrice Bellard, et
>> al.
>>   configuration: --enable-shared --disable-static --cpu=prescott
>> --extra-cflags=-DX_DISPLAY_MISSING -I/usr/local/include -include
>> llrint.h --extra-ldflags=-L/usr/local/lib --extra-libs=-l llrint
>> --enable-gpl --enable-nonfree --enable-libamr-nb --enable-libamr-wb
>> --enable-swscale --enable-avfilter --enable-avfilter-lavf
>> --enable-pthreads --enable-avisynth --enable-bzlib --enable-libfaac
>> --enable-libgsm --enable-libmp3lame --enable-libtheora
>> --enable-libx264 --enable-zlib --build-suffix=-SVN
>>   libavutil     49.15. 0 / 49.15. 0
>>   libavcodec    52.18. 0 / 52.18. 0
>>   libavformat   52.29. 2 / 52.29. 2
>>   libavdevice   52. 1. 0 / 52. 1. 0
>>   libavfilter    0. 4. 0 /  0. 4. 0
>>   libswscale     0. 7. 1 /  0. 7. 1
>>   built on Feb 25 2009 11:41:58, gcc: 4.2.4
>>
>> Seems stream 0 codec frame rate differs from container frame rate:
>> 30000.00 (30000/1) -> 25.00 (25/1)
>> Input #0, avi, from 'in.avi':
>>   Duration: 00:01:00.03, start: 0.000000, bitrate: 822 kb/s
>>     Stream #0.0: Video: mpeg4, yuv420p, 640x352 [PAR 1:1 DAR 20:11],
>> 25
>> tbr, 25 tbn, 30k tbc
>>     Stream #0.1: Audio: mp3, 22050 Hz, stereo, s16, 56 kb/s
>> Output #0, avi, to 'out_fps1.avi':
>>     Stream #0.0: Video: mpeg4, yuv420p, 640x352 [PAR 1:1 DAR 20:11],
>> q=2-31, 200 kb/s, 90k tbn, 25 tbc
>> Stream mapping:
>>   Stream #0.0 -> #0.0
>> Press [q] to stop encoding
>> frame=   60 fps= 35 q=6.9 Lsize=     292kB time=59.04 bitrate=
>> 40.5kbits/s video:252kB audio:0kB global headers:0kB muxing overhead
>> 16.000823%
>>
>>
>> The out_fps1.avi has 60 frames, as expected, but VirtualDub believes
>> has 1476 frames due to the 25 tbc probably. GSpot reports 60 frames.
>> ffmpeg is also confused and ffmpeg -i out_fps1.avi out%04d.png
>> produces 1475 PNGs.
>>
>>
>> ffmpeg  -i in.avi -vfilters fps=1 -r 1  -y -an out_fps1_r1.avi
>>
>> The out_fps1_r1.avi has 60 frames, works fine in VirtualDub, GSpot,
>> ffmpeg.
>
> all mostly as expected, did you expect anything else?

Well, since avfilters may drop/add frames and alter timestamps, there
should be some way to tell ffmpeg to avoid sync'ing against the
original input stream.
-r is a way, but it then forces a fixed rate.

> btw none of this is really related to lavfi, and just to make it clear
> is in no way a reason to hold up lavi integration

Right, it looks more ffmpeg that lavfi related.

Regards,
V?ctor