[FFmpeg-devel] [libav-devel] mpegts encoder not interleaving audio/video packets well

[Tony Strauss]

On Thu, Jun 16, 2011 at 12:09 PM, Michael Niedermayer <michaelni at gmx.at>wrote:

> On Thu, Jun 16, 2011 at 12:05:34PM -0400, Tony Strauss wrote:
> >
> > I took a look through the mpeg ps encoder (libavformat/mpegenc.c).  It
> seems
> > to require interleaving within .7 sec by default (max_delay).  I think
> that
> > it's reasonable to implement this for the mpegts muxer as well.
>  max_delay
> > also is configurable via ffmpeg's command-line, so people can set it to
> be
> > whatever they want.  I can create a patch for this, if it sounds
> reasonable
> > to everyone.
>
> sounds reasonable to me

I've attached a patch (reproduced below as well).  The tests continue to
pass with it.

While testing, I noticed a block of code in the mpegts encoder that struck
me as strange (mpegtsenc.c:885):
    const uint64_t delay = av_rescale(s->max_delay, 90000, AV_TIME_BASE)*2;
    int64_t dts = AV_NOPTS_VALUE, pts = AV_NOPTS_VALUE;

    if (pkt->pts != AV_NOPTS_VALUE)
        pts = pkt->pts + delay;
    if (pkt->dts != AV_NOPTS_VALUE)
        dts = pkt->dts + delay;

The pts and dts of all of the packets gets incremented by twice max_delay,
which seems contrary to its use in the mpeg ps muxer (although I may well be
missing something).

diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
index 7e96472..cbc194c 100644
--- a/libavformat/mpegtsenc.c
+++ b/libavformat/mpegtsenc.c
@@ -878,6 +878,7 @@ static int mpegts_write_packet(AVFormatContext *s,
AVPacket *pkt)
     uint8_t *buf= pkt->data;
     uint8_t *data= NULL;
     MpegTSWriteStream *ts_st = st->priv_data;
+    const uint64_t max_delay = av_rescale(s->max_delay, 90000,
AV_TIME_BASE);
     const uint64_t delay = av_rescale(s->max_delay, 90000, AV_TIME_BASE)*2;
     int64_t dts = AV_NOPTS_VALUE, pts = AV_NOPTS_VALUE;

@@ -947,6 +948,18 @@ static int mpegts_write_packet(AVFormatContext *s,
AVPacket *pkt)
         }
     }

+    /*
+     * Flush the audio packets once we've amassed a full PES payload or
+     * once the stream has moved a certain amount of time past the first
audio
+     * packet in the buffer.
+     */
+    if ((ts_st->payload_index + size > DEFAULT_PES_PAYLOAD_SIZE) ||
+        ((ts_st->payload_index > 0) && (dts - ts_st->payload_dts >
max_delay))) {
+        mpegts_write_pes(s, st, ts_st->payload, ts_st->payload_index,
+                         ts_st->payload_pts, ts_st->payload_dts);
+        ts_st->payload_index = 0;
+    }
+
     if (st->codec->codec_type != AVMEDIA_TYPE_AUDIO) {
         // for video and subtitle, write a single pes packet
         mpegts_write_pes(s, st, buf, size, pts, dts);
@@ -954,12 +967,6 @@ static int mpegts_write_packet(AVFormatContext *s,
AVPacket *pkt)
         return 0;
     }

-    if (ts_st->payload_index + size > DEFAULT_PES_PAYLOAD_SIZE) {
-        mpegts_write_pes(s, st, ts_st->payload, ts_st->payload_index,
-                         ts_st->payload_pts, ts_st->payload_dts);
-        ts_st->payload_index = 0;
-    }
-
     if (!ts_st->payload_index) {
         ts_st->payload_pts = pts;
         ts_st->payload_dts = dts;


Tony
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