[libav-commits] movenc: Allow setting start_dts/start_cts before writing actual packets

Martin Storsjö git at libav.org
Wed Nov 11 21:58:42 CET 2015


Module: libav
Branch: master
Commit: bef3b1f59f036aba4a5fe599b2480f6bd9e6b280

Author:    Martin Storsjö <martin at martin.st>
Committer: Martin Storsjö <martin at martin.st>
Date:      Tue Nov  3 22:16:21 2015 +0200

movenc: Allow setting start_dts/start_cts before writing actual packets

By writing a zero-sized packet, the caller can communicate the
start_dts/start_cts for the stream without actually writing
the first packet.

This allows doing random-access writing of fragments when the
start dts of the stream isn't zero, so that the edit list in the moov
is written based on timestamps from the nominal start time signaled
via the zero-sized packet, while the first proper packet written
corresponds to a later fragment.

To avoid potential unexpected behaviour, empty packets only set
start_dts if the frag_discont flag is set.

Signed-off-by: Martin Storsjö <martin at martin.st>

---

 libavformat/movenc.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index ac452b1..9f7cca9 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -3585,9 +3585,6 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
         int64_t frag_duration = 0;
         int size = pkt->size;
 
-        if (!pkt->size)
-            return 0;             /* Discard 0 sized packets */
-
         if (mov->flags & FF_MOV_FLAG_FRAG_DISCONT) {
             int i;
             for (i = 0; i < s->nb_streams; i++)
@@ -3595,6 +3592,18 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
             mov->flags &= ~FF_MOV_FLAG_FRAG_DISCONT;
         }
 
+        if (!pkt->size) {
+            if (trk->start_dts == AV_NOPTS_VALUE && trk->frag_discont) {
+                trk->start_dts = pkt->dts;
+                if (pkt->pts != AV_NOPTS_VALUE)
+                    trk->start_cts = pkt->pts - pkt->dts;
+                else
+                    trk->start_cts = 0;
+            }
+
+            return 0;             /* Discard 0 sized packets */
+        }
+
         if (trk->entry)
             frag_duration = av_rescale_q(pkt->dts - trk->cluster[0].dts,
                                          s->streams[pkt->stream_index]->time_base,



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