[FFmpeg-devel] [PATCH] make stream-switching work with MOV demuxer

[Reimar Döffinger]

On Tue, Jun 23, 2009 at 11:17:02AM -0700, Baptiste Coudurier wrote:
> Reimar D?ffinger wrote:
> > Hello,
> > currently the MOV demuxer does not even keep track of the "current"
> > position of streams set to AVDISCARD_ALL.
> > This means that when removing AVDISCARD_ALL, that stream will start
> > playing from the beginning.
> > Now, the current behaviour may be valid, but it is at least inconsistent
> > with most other demuxers, and at least with the current seeking API I
> > can not see how else it should be possible to seamlessly switch between
> > e.g. different audio streams.
> > Since it duplicates code, attached patch is hardly acceptable, but it
> > fixes the issue...
> 
> Just do like the stream wasn't discarded, just don't read the sample,
> and retry. It should avoid code duplication I think.

Yes, that is possible, it still seems a bit ugly and messy.
I also thought about moving the whole pts calculation etc. up, but
that does not work because dv_produce_packet would then overwrite the
values.
-------------- next part --------------
Index: libavformat/mov.c
===================================================================
--- libavformat/mov.c	(revision 19256)
+++ libavformat/mov.c	(working copy)
@@ -1981,14 +1981,16 @@
 {
     MOVContext *mov = s->priv_data;
     MOVStreamContext *sc = 0;
-    AVIndexEntry *sample = 0;
+    AVIndexEntry *sample;
     int64_t best_dts = INT64_MAX;
+    int discard = 0;
     int i, ret;
  retry:
+    sample = NULL;
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
         MOVStreamContext *msc = st->priv_data;
-        if (st->discard != AVDISCARD_ALL && msc->pb && msc->current_sample < st->nb_index_entries) {
+        if (msc->pb && msc->current_sample < st->nb_index_entries) {
             AVIndexEntry *current_sample = &st->index_entries[msc->current_sample];
             int64_t dts = av_rescale(current_sample->timestamp, AV_TIME_BASE, msc->time_scale);
             dprintf(s, "stream %d, sample %d, dts %"PRId64"\n", i, msc->current_sample, dts);
@@ -2000,6 +2002,7 @@
                 sample = current_sample;
                 best_dts = dts;
                 sc = msc;
+                discard = st->discard == AVDISCARD_ALL;
             }
         }
     }
@@ -2014,6 +2017,7 @@
     }
     /* must be done just before reading, to avoid infinite loop on sample */
     sc->current_sample++;
+    if (!discard) {
     if (url_fseek(sc->pb, sample->pos, SEEK_SET) != sample->pos) {
         av_log(mov->fc, AV_LOG_ERROR, "stream %d, offset 0x%"PRIx64": partial file\n",
                sc->ffindex, sample->pos);
@@ -2031,6 +2035,7 @@
             return -1;
     }
 #endif
+    }
     pkt->stream_index = sc->ffindex;
     pkt->dts = sample->timestamp;
     if (sc->ctts_data) {
@@ -2051,6 +2056,7 @@
         pkt->duration = next_dts - pkt->dts;
         pkt->pts = pkt->dts;
     }
+    if (discard) goto retry;
     pkt->flags |= sample->flags & AVINDEX_KEYFRAME ? PKT_FLAG_KEY : 0;
     pkt->pos = sample->pos;
     dprintf(s, "stream %d, pts %"PRId64", dts %"PRId64", pos 0x%"PRIx64", duration %d\n",
@@ -2108,7 +2114,7 @@
 
     for (i = 0; i < s->nb_streams; i++) {
         st = s->streams[i];
-        if (stream_index == i || st->discard == AVDISCARD_ALL)
+        if (stream_index == i)
             continue;
 
         timestamp = av_rescale_q(seek_timestamp, s->streams[stream_index]->time_base, st->time_base);