- if (subs.empty() || period.from < subs.front()->period().from || period.to > (subs.back()->period().to + ContentTime::from_seconds (10))) {
- /* Either we have no decoded data, or what we do have is a long way from what we want: seek */
- seek (period.from, true);
+ /* Seek if what we want is before what we have, or a more than a little bit after.
+ Be careful with the length of this `little bit'; consider the case where the last
+ subs were just less than this little bit B ago. Then we will not seek, but instead
+ pass() for nearly B seconds; if we are a FFmpegDecoder then this will generate B's
+ worth of video which will stack up. If B + the pre-roll is bigger than the maximum
+ number of frames that the VideoDecoder will keep then we will get an assertion
+ failure in VideoDecoder.
+ */
+ if (subs.empty() || sp.back().to < subs.front().period().from || sp.front().from > (subs.back().period().to + ContentTime::from_seconds (1))) {
+ seek (sp.front().from, true);