[FFmpeg-trac] #2248(avfilter:new): select filter does not correctly set prev_pts
FFmpeg
trac at avcodec.org
Thu Feb 7 19:13:46 CET 2013
#2248: select filter does not correctly set prev_pts
-------------------------------------+-------------------------------------
Reporter: schmod | Type: defect
Status: new | Priority: normal
Component: avfilter | Version: git-
Keywords: select | master
aselect filter avfilter | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
When using the select filter, the filter's internal `pts` variable is
always equal to `prev_pts`. This is presumably not the intended (or a
useful) behavior.
One would expect that `prev_pts` should always be equal to the pts of the
last frame that was processed (but not necessarily chosen) by the select
filter.
For instance, if I filter a video for frames where the `pts` is equal to
`prev_pts`:
{{{
ffmpeg -i big_buck_bunny_480p_surround-fix.avi -vf
select='eq(prev_pts\,pts)',showinfo -frames:v 50 out.avi
ffmpeg version N-49610-gc2dd5a1 Copyright (c) 2000-2013 the FFmpeg
developers
built on Feb 5 2013 13:26:02 with gcc 4.7.2 (GCC)
}}}
I get back the original video, rather than nothing at all (which is what
you would expect).
Poking around in the source (f_select.c), I see that the values for `PTS`
and `PREV_PTS` are both set in (basically) the same place. Presumably,
`PREV_PTS` should only be set *after* the filter has decided whether to
select or discard the current frame?
{{{
273 select->var_values[VAR_PTS] = TS2D(ref->pts);
274 select->var_values[VAR_T ] = TS2D(ref->pts) *
av_q2d(inlink->time_base);
275 select->var_values[VAR_POS] = ref->pos == -1 ? NAN : ref->pos;
276 select->var_values[VAR_PREV_PTS] = TS2D(ref ->pts);
}}}
[http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavfilter/f_select.c;h=4881a85ece8717d49d592a21699cfa1f2ded2b4e;hb=HEAD#l273]
Note that I'm running ffmpeg on Windows, although this does not appear to
be a platform-specific bug.
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2248>
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