libav: fix mkv seek crash

Remove hopelessly broken code that attempted to rewind the seek point to
a position in the file where subtitles in every subtitle track after
the seek time are after the computed position.

(cherry picked from commit 380059d4d8cf245e3667a5c92159f7b294d682ac)

diff --git a/contrib/ffmpeg/A13-mkv-fix-seek-crash.patch b/contrib/ffmpeg/A13-mkv-fix-seek-crash.patch
new file mode 100644 (file)
index 0000000..3563855
--- /dev/null
+++ b/contrib/ffmpeg/A13-mkv-fix-seek-crash.patch
@@ -0,0 +1,57 @@
+From 4b73e7f3606fe0a33c258c802998b4e24ae24fb0 Mon Sep 17 00:00:00 2001
+From: John Stebbins <stebbins@jetheaddev.com>
+Date: Tue, 21 Feb 2017 15:14:51 -0700
+Subject: [PATCH] matroskadec: remove broken subtitle seek code
+
+It looks up an index on one stream, and then uses that index on a
+different stream.  If nb_index_entries is different on the streams,
+kaboom!
+---
+ libavformat/matroskadec.c | 16 ++--------------
+ 1 file changed, 2 insertions(+), 14 deletions(-)
+
+diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
+index 4e121b6..d88088a 100644
+--- a/libavformat/matroskadec.c
++++ b/libavformat/matroskadec.c
+@@ -2693,7 +2693,7 @@ static int matroska_read_seek(AVFormatContext *s, int stream_index,
+     MatroskaDemuxContext *matroska = s->priv_data;
+     MatroskaTrack *tracks = NULL;
+     AVStream *st = s->streams[stream_index];
+-    int i, index, index_sub, index_min;
++    int i, index;
+ 
+     /* Parse the CUES now since we need the index data to seek. */
+     if (matroska->cues_parsing_deferred) {
+@@ -2720,27 +2720,15 @@ static int matroska_read_seek(AVFormatContext *s, int stream_index,
+     if (index < 0)
+         return 0;
+ 
+-    index_min = index;
+     tracks = matroska->tracks.elem;
+     for (i = 0; i < matroska->tracks.nb_elem; i++) {
+         tracks[i].audio.pkt_cnt        = 0;
+         tracks[i].audio.sub_packet_cnt = 0;
+         tracks[i].audio.buf_timecode   = AV_NOPTS_VALUE;
+         tracks[i].end_timecode         = 0;
+-        if (tracks[i].type == MATROSKA_TRACK_TYPE_SUBTITLE &&
+-            tracks[i].stream->discard != AVDISCARD_ALL) {
+-            index_sub = av_index_search_timestamp(
+-                tracks[i].stream, st->index_entries[index].timestamp,
+-                AVSEEK_FLAG_BACKWARD);
+-            if (index_sub >= 0 &&
+-                st->index_entries[index_sub].pos < st->index_entries[index_min].pos &&
+-                st->index_entries[index].timestamp -
+-                st->index_entries[index_sub].timestamp < 30000000000 / matroska->time_scale)
+-                index_min = index_sub;
+-        }
+     }
+ 
+-    avio_seek(s->pb, st->index_entries[index_min].pos, SEEK_SET);
++    avio_seek(s->pb, st->index_entries[index].pos, SEEK_SET);
+     matroska->current_id       = 0;
+     matroska->skip_to_keyframe = !(flags & AVSEEK_FLAG_ANY);
+     matroska->skip_to_timecode = st->index_entries[index].timestamp;
+-- 
+2.9.3
+