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demux: attempt to accurately reflect seek range with muxed subtitles

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If subtitles are part of the stream, determining the seekable range
becomes harder. Subtitles are sparse, and can have packets in irregular
intervals, or even completely lack packets. The usual logic of computing
the seek range by the min/max packet timestamps fails.

Solve this by making the only assumption we can make: subtitle packets
are implicitly demuxed along with other packets. We also assume perfect
interleaving for this, but you really can't do anything with sparse
packets that makes sense without this assumption.

One special case is if we prune sparse packets within the current
seekable range. Obviously this should limit the seekable range to after
the pruned packet.
This commit is contained in:
wm4 2017-11-10 08:57:37 +01:00
parent 7c1e7468e6
commit ed1af99727
1 changed files with 33 additions and 5 deletions
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38
demux/demux.c
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@ -233,6 +233,7 @@ struct demux_queue {
// incrementally maintained seek range, possibly invalid
double seek_start, seek_end;
double last_pruned; // timestamp of last pruned keyframe
};
struct demux_stream {
@ -393,19 +394,43 @@ static void update_seek_ranges(struct demux_cached_range *range)
for (int n = 0; n < range->num_streams; n++) {
struct demux_queue *queue = range->streams[n];
if (queue->ds->selected) {
if (queue->ds->selected && queue->ds->eager) {
range->seek_start = MP_PTS_MAX(range->seek_start, queue->seek_start);
range->seek_end = MP_PTS_MIN(range->seek_end, queue->seek_end);
if (queue->seek_start == MP_NOPTS_VALUE ||
queue->seek_end == MP_NOPTS_VALUE)
{
if (queue->seek_start >= queue->seek_end) {
range->seek_start = range->seek_end = MP_NOPTS_VALUE;
break;
}
}
}
// Sparse stream behavior is not very clearly defined, but usually we don't
// want it to restrict the range of other streams, unless
// This is incorrect in any of these cases:
// - sparse streams only (it's unknown how to determine an accurate range)
// - if sparse streams have non-keyframe packets (we set queue->last_pruned
// to the start of the pruned keyframe range - we'd need the end or so)
// We also assume that ds->eager equals to a stream being sparse (usually
// true, except if only sparse streams are selected).
// We also rely on the fact that the demuxer position will always be ahead
// of the seek_end for audio/video, because they need to prefetch at least
// 1 packet to detect the end of a keyframe range. This means that we're
// relatively guaranteed to have all sparse (subtitle) packets within the
// seekable range.
for (int n = 0; n < range->num_streams; n++) {
struct demux_queue *queue = range->streams[n];
if (queue->ds->selected && !queue->ds->eager &&
queue->last_pruned != MP_NOPTS_VALUE)
{
// (last_pruned is _exclusive_ to the seekable range, so add a small
// value to exclude it from the valid range.)
range->seek_start =
MP_PTS_MAX(range->seek_start, queue->last_pruned + 0.1);
}
}
if (range->seek_start >= range->seek_end)
range->seek_start = range->seek_end = MP_NOPTS_VALUE;
}
@ -459,7 +484,7 @@ static void clear_queue(struct demux_queue *queue)
queue->head = queue->tail = NULL;
queue->next_prune_target = NULL;
queue->keyframe_latest = NULL;
queue->seek_start = queue->seek_end = MP_NOPTS_VALUE;
queue->seek_start = queue->seek_end = queue->last_pruned = MP_NOPTS_VALUE;
queue->correct_dts = queue->correct_pos = true;
queue->last_pos = -1;
@ -933,6 +958,7 @@ static void attempt_range_joining(struct demux_internal *in)
}
q2->next_prune_target = q1->next_prune_target;
q2->seek_start = q1->seek_start;
q2->last_pruned = q1->last_pruned;
q2->correct_dts &= q1->correct_dts;
q2->correct_pos &= q1->correct_pos;
@ -1253,6 +1279,8 @@ static void prune_old_packets(struct demux_internal *in)
if (in->seekable_cache && !queue->next_prune_target) {
// (Has to be _after_ queue->head to drop at least 1 packet.)
struct demux_packet *prev = queue->head;
if (queue->seek_start != MP_NOPTS_VALUE)
queue->last_pruned = queue->seek_start;
queue->seek_start = MP_NOPTS_VALUE;
queue->next_prune_target = queue->tail; // (prune all if none found)
while (prev->next) {