movenc: Write track durations with all bits set if duration is unknown

According to 14496-12, the duration should be all 1s if
the duration is unknown. This is the case if writing a moov
atom without any samples described in it (e.g. as in ismv files).
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/movenc.c

@@ -1317,7 +1317,10 @@ static int mov_write_mdhd_tag(AVIOContext *pb, MOVTrack *track)
         avio_wb32(pb, track->time); /* modification time */
     }
     avio_wb32(pb, track->timescale); /* time scale (sample rate for audio) */
-    (version == 1) ? avio_wb64(pb, track->track_duration) : avio_wb32(pb, track->track_duration); /* duration */
+    if (!track->entry)
+        (version == 1) ? avio_wb64(pb, UINT64_C(0xffffffffffffffff)) : avio_wb32(pb, 0xffffffff);
+    else
+        (version == 1) ? avio_wb64(pb, track->track_duration) : avio_wb32(pb, track->track_duration); /* duration */
     avio_wb16(pb, track->language); /* language */
     avio_wb16(pb, 0); /* reserved (quality) */
 
@@ -1361,7 +1364,10 @@ static int mov_write_tkhd_tag(AVIOContext *pb, MOVTrack *track, AVStream *st)
     }
     avio_wb32(pb, track->track_id); /* track-id */
     avio_wb32(pb, 0); /* reserved */
-    (version == 1) ? avio_wb64(pb, duration) : avio_wb32(pb, duration);
+    if (!track->entry)
+        (version == 1) ? avio_wb64(pb, UINT64_C(0xffffffffffffffff)) : avio_wb32(pb, 0xffffffff);
+    else
+        (version == 1) ? avio_wb64(pb, duration) : avio_wb32(pb, duration);
 
     avio_wb32(pb, 0); /* reserved */
     avio_wb32(pb, 0); /* reserved */