[FFmpeg-devel] [PATCH] ffmpeg: prevent premature EOF in sub2video with nullptr AVSubtitles

[Paul B Mahol]

On 3/31/18, Jan Ekstroem <jeebjp at gmail.com> wrote:
> With certain types of input and the filter chain getting re-initialized
> or re-configured, multiple nullptr AVSubtitles can get pushed into
> sub2video_update() in a row from sub2video_heartbeat.
>
> This causes end_pts, and on the next round pts, to become INT64_MAX,
> latter of which signals EOF in framesync, leading to complete loss of
> subtitles from that point on.
>
> Thus, check that the sub2video.end_pts is smaller than INT64_MAX
> in a similar fashion to sub2video_flush before sending out the
> nullptr AVSubtitle. This keeps premature EOFs from happening in
> framesync and the subtitle overlay is kept past the filter chain
> re-initializations/configurations.
> ---
> Alternative patch to the first one, not really a v2 so not marking
> it as such.
>
> The initial patch tried to still pass on the updates but keeping the
> end_pts from becoming INT64_MAX (as it would get utilized as the pts
> for the next packet). This changed the sub2video FATE test's
> results as well as made the theoretical secondary stream not being
> possible to EOF with nullptr AVSubtitles. That said, I am not sure
> if the test's changes or the change in capability to do such
> EOF'ification  were explicitly incorrect, but clearly my knowledge in
> this area was not perfect and the change in FATE test probably kept
> everyone away from the initial patch. For the record, the initial patch
> worked for way more than 48h without seeming problems with a CFR stream,
> so the previous patch was not as if not tested.
>
> Thus, this alternative patch instead opts to never send out new nullptr
> AVSubtitle updates if end_pts is already at INT64_MAX. The FATE test
> also is unchanged.
> ---
>  fftools/ffmpeg.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>

lgtm