Add skip_to_keyframe stream variable.

This replaces the matroskadec one with the same name.
The advantage is not only easier reuse in other demuxers
but also that we can make the decisions after the parser.
This fixes seeking in files that mark the keyframes incorrectly,
for example the file in track ticket #1003.
The matroska variable is still kept to be able to complain
about such broken files.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavformat/avformat.h

@@ -787,6 +787,11 @@ typedef struct AVStream {
      * NOT PART OF PUBLIC API
      */
     int request_probe;
+    /**
+     * Indicates that everything up to the next keyframe
+     * should be discarded.
+     */
+    int skip_to_keyframe;
 } AVStream;
 
 #define AV_PROGRAM_RUNNING 1

libavformat/matroskadec.c

@@ -1839,9 +1839,14 @@ static int matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data,
     }
 
     if (matroska->skip_to_keyframe && track->type != MATROSKA_TRACK_TYPE_SUBTITLE) {
-        if (!is_keyframe || timecode < matroska->skip_to_timecode)
+        if (timecode < matroska->skip_to_timecode)
             return res;
-        matroska->skip_to_keyframe = 0;
+        if (!st->skip_to_keyframe) {
+            av_log(matroska->ctx, AV_LOG_ERROR, "File is broken, keyframes not correctly marked!\n");
+            matroska->skip_to_keyframe = 0;
+        }
+        if (is_keyframe)
+            matroska->skip_to_keyframe = 0;
     }
 
     switch ((flags & 0x06) >> 1) {
@@ -2147,6 +2152,7 @@ static int matroska_read_seek(AVFormatContext *s, int stream_index,
 
     avio_seek(s->pb, st->index_entries[index_min].pos, SEEK_SET);
     matroska->current_id = 0;
+    st->skip_to_keyframe =
     matroska->skip_to_keyframe = !(flags & AVSEEK_FLAG_ANY);
     matroska->skip_to_timecode = st->index_entries[index].timestamp;
     matroska->done = 0;
@@ -2158,6 +2164,7 @@ err:
     // the generic seeking code.
     matroska_clear_queue(matroska);
     matroska->current_id = 0;
+    st->skip_to_keyframe =
     matroska->skip_to_keyframe = 0;
     matroska->done = 0;
     matroska->num_levels = 0;

libavformat/utils.c

@@ -1315,6 +1315,12 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
             /* free packet */
             av_free_packet(&cur_pkt);
         }
+        if (pkt->flags & AV_PKT_FLAG_KEY)
+            st->skip_to_keyframe = 0;
+        if (st->skip_to_keyframe) {
+            av_free_packet(&cur_pkt);
+            got_packet = 0;
+        }
     }
 
     if (!got_packet && s->parse_queue)