lavf: Add support offset timestamps on muxing.

This allows avoiding negative timestamps.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -832,6 +832,13 @@ typedef struct AVStream {
      * its lifetime differs from info which is why its not in that structure.
      */
     int nb_decoded_frames;
+
+    /**
+     * Timestamp offset added to timestamps before muxing
+     * NOT PART OF PUBLIC API
+     */
+    int64_t mux_ts_offset;
+
 } AVStream;
 
 #define AV_PROGRAM_RUNNING 1
@@ -1111,6 +1118,17 @@ typedef struct AVFormatContext {
      */
     int use_wallclock_as_timestamps;
 
+    /**
+     * Avoids negative timestamps during muxing
+     *  0 -> allow negative timestamps
+     *  1 -> avoid negative timestamps
+     * -1 -> choose automatically (default)
+     * Note, this is only works when interleave_packet_per_dts is in use
+     * - encoding: Set by user via AVOptions (NO direct access)
+     * - decoding: unused
+     */
+    int avoid_negative_ts;
+
     /*****************************************************************
      * All fields below this line are not part of the public API. They
      * may not be used outside of libavformat and can be changed and

libavformat/options_table.h

@@ -71,6 +71,7 @@ static const AVOption options[]={
 {"compliant",  "consider all spec non compliancies as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_COMPLIANT }, INT_MIN, INT_MAX, D, "err_detect"},
 {"aggressive", "consider things that a sane encoder shouldnt do as an error", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_AGGRESSIVE }, INT_MIN, INT_MAX, D, "err_detect"},
 {"use_wallclock_as_timestamps", "use wallclock as timestamps", OFFSET(use_wallclock_as_timestamps), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, D},
+{"avoid_negative_ts", "avoid negative timestamps", OFFSET(avoid_negative_ts), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 1, E},
 {NULL},
 };
 

libavformat/utils.c

@@ -3699,16 +3699,36 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
         }
     }
     if(stream_count && flush){
+        AVStream *st;
         pktl= s->packet_buffer;
         *out= pktl->pkt;
+        st = s->streams[out->stream_index];
 
         s->packet_buffer= pktl->next;
         if(!s->packet_buffer)
             s->packet_buffer_end= NULL;
 
-        if(s->streams[out->stream_index]->last_in_packet_buffer == pktl)
-            s->streams[out->stream_index]->last_in_packet_buffer= NULL;
+        if(st->last_in_packet_buffer == pktl)
+            st->last_in_packet_buffer= NULL;
         av_freep(&pktl);
+
+        if (s->avoid_negative_ts > 0) {
+            if (out->dts != AV_NOPTS_VALUE) {
+                if (!st->mux_ts_offset && out->dts < 0) {
+                    for(i=0; i < s->nb_streams; i++) {
+                        s->streams[i]->mux_ts_offset =
+                            av_rescale_q_rnd(-out->dts,
+                                             st->time_base,
+                                             s->streams[i]->time_base,
+                                             AV_ROUND_UP);
+                    }
+                }
+                out->dts += st->mux_ts_offset;
+            }
+            if (out->pts != AV_NOPTS_VALUE)
+                out->pts += st->mux_ts_offset;
+        }
+
         return 1;
     }else{
         av_init_packet(out);

libavformat/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 54
-#define LIBAVFORMAT_VERSION_MINOR 28
+#define LIBAVFORMAT_VERSION_MINOR 29
 #define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \