qtdemux: fix key unit seek corner case

If a key unit seek is performed with a time position that matches
the offset of a keyframe, but not its actual PTS, we need to
adjust the segment nevertheless.

For example consider the following case:

* stream starts with a keyframe at 0 nanosecond, lasting 40 milliseconds
* user does a key unit seek at 20 milliseconds
* we don't adjust the segment as the time position is "over" a keyframe
* we push a segment that starts at 20 milliseconds
* we push a buffer with PTS == 0
* an element downstream (eg rtponviftimestamp) tries to calculate the
  stream time of the buffer, fails to do so and drops it

diff --git a/gst/isomp4/qtdemux.c b/gst/isomp4/qtdemux.c
index f9c8383..ad2192a 100644 (file)
--- a/gst/isomp4/qtdemux.c
+++ b/gst/isomp4/qtdemux.c
@@ -1394,9 +1394,10 @@ gst_qtdemux_adjust_seek (GstQTDemux * qtdemux, gint64 desired_time,
       if (next && kindex == -1)
         kindex = gst_qtdemux_find_keyframe (qtdemux, str, index, FALSE);
 
-      /* if the keyframe is at a different position, we need to update the
-       * requested seek time */
-      if (index != kindex) {
+      /* Update the requested time whenever a keyframe was found, to make it
+       * accurate and avoid having the first buffer fall outside of the segment
+       */
+      if (kindex != -1) {
         index = kindex;
 
         /* get timestamp of keyframe */