demux: improve and optimize cache pruning and seek range determination

The main purpose of this commit is avoiding any hidden O(n^2) algorithms
in the code for pruning the demuxer cache, and for determining the
seekable boundaries of the cache. The old code could loop over the whole
packet queue on every packet pruned in certain corner cases.

There are two ways how to reach the goal:
 1) commit a cardinal sin
 2) do everything incrementally

The cardinal sin is adding an extra field to demux_packet, which caches
the determined seekable range for a keyframe range. demux_packet is a
rather general data structure and thus shouldn't have any fields that
are not inherent to its use, and are only needed as an implementation
detail of code using it. But what are you gonna do, sue me?

In the future, demux.c might have its own packet struct though. Then the
other existing cardinal sin (the "next" field, from MPlayer times) could
be removed as well.

This commit also changes slightly how the seek end is determined. There
is a note on the manpage in case anyone finds the new behavior
confusing. It's somewhat cleaner and  might be needed for supporting
multiple ranges (although that's unclear).

1 files changed, 1 insertions, 0 deletions

diff --git a/demux/packet.c b/demux/packet.c
index 0a13b0e6a5..156222737c 100644
--- a/demux/packet.c
+++ b/demux/packet.c
@@ -54,6 +54,7 @@ struct demux_packet *new_demux_packet_from_avpacket(struct AVPacket *avpkt)
         .end = MP_NOPTS_VALUE,
         .stream = -1,
         .avpacket = talloc_zero(dp, AVPacket),
+        .kf_seek_pts = MP_NOPTS_VALUE,
     };
     av_init_packet(dp->avpacket);
     int r = -1;