avformat: extracting NTP timestamp from RTCP

For muxing, it accepts
both 0 and AV_NOPTS_VALUE. For demuxing, it will present
AV_NOPTS_VALUE when start_time_realtime is unknown.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/APIchanges

@@ -15,6 +15,9 @@ libavutil:     2012-10-22
 
 API changes, most recent first:
 
+2014-03-11 - xxxxxxx - lavf 55.34.101 - avformat.h
+  Set AVFormatContext.start_time_realtime when demuxing.
+
 2014-xx-xx - xxxxxx - lavd 55.11.100 - avdevice.h
   Add av_input_audio_device_next().
   Add av_input_video_device_next().

libavformat/avformat.h

@@ -1275,7 +1275,12 @@ typedef struct AVFormatContext {
      * Start time of the stream in real world time, in microseconds
      * since the Unix epoch (00:00 1st January 1970). That is, pts=0 in the
      * stream was captured at this real world time.
-     * Muxing only, set by the caller before avformat_write_header().
+     * - muxing: Set by the caller before avformat_write_header(). If set to
+     *           either 0 or AV_NOPTS_VALUE, then the current wall-time will
+     *           be used.
+     * - demuxing: Set by libavformat. AV_NOPTS_VALUE if unknown. Note that
+     *             the value may become known after some number of frames
+     *             have been received.
      */
     int64_t start_time_realtime;
 

libavformat/options_table.h

@@ -57,6 +57,7 @@ static const AVOption avformat_options[] = {
 {"fdebug", "print specific debug info", OFFSET(debug), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, INT_MAX, E|D, "fdebug"},
 {"ts", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_FDEBUG_TS }, INT_MIN, INT_MAX, E|D, "fdebug"},
 {"max_delay", "maximum muxing or demuxing delay in microseconds", OFFSET(max_delay), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, INT_MAX, E|D},
+{"start_time_realtime", "wall-clock time when stream begins (PTS==0)", OFFSET(start_time_realtime), AV_OPT_TYPE_INT64, {.i64 = AV_NOPTS_VALUE}, INT64_MIN, INT64_MAX, E},
 {"fpsprobesize", "number of frames used to probe fps", OFFSET(fps_probe_size), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX-1, D},
 {"audio_preload", "microseconds by which audio packets should be interleaved earlier", OFFSET(audio_preload), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E},
 {"chunk_duration", "microseconds for each chunk", OFFSET(max_chunk_duration), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E},

libavformat/rtpenc.c

@@ -119,7 +119,7 @@ static int rtp_write_header(AVFormatContext *s1)
         s->ssrc = av_get_random_seed();
     s->first_packet = 1;
     s->first_rtcp_ntp_time = ff_ntp_time();
-    if (s1->start_time_realtime)
+    if (s1->start_time_realtime != 0  &&  s1->start_time_realtime != AV_NOPTS_VALUE)
         /* Round the NTP time to whole milliseconds. */
         s->first_rtcp_ntp_time = (s1->start_time_realtime / 1000) * 1000 +
                                  NTP_OFFSET_US;

libavformat/rtsp.c

@@ -2071,6 +2071,16 @@ redo:
                             st2->time_base);
                     }
                 }
+                // Make real NTP start time available in AVFormatContext
+                if (s->start_time_realtime == AV_NOPTS_VALUE) {
+                    s->start_time_realtime = av_rescale (rtpctx->first_rtcp_ntp_time - (NTP_OFFSET << 32), 1000000, 1LL << 32);
+                    if (rtpctx->st) {
+                        s->start_time_realtime -=
+                            av_rescale (rtpctx->rtcp_ts_offset,
+                                        (uint64_t) rtpctx->st->time_base.num * 1000000,
+                                                   rtpctx->st->time_base.den);
+                    }
+                }
             }
             if (ret == -RTCP_BYE) {
                 rt->nb_byes++;

libavformat/rtspenc.c

@@ -51,6 +51,7 @@ int ff_rtsp_setup_output_streams(AVFormatContext *s, const char *addr)
     char *sdp;
     AVFormatContext sdp_ctx, *ctx_array[1];
 
+    if (s->start_time_realtime == 0  ||  s->start_time_realtime == AV_NOPTS_VALUE)
         s->start_time_realtime = av_gettime();
 
     /* Announce the stream */

libavformat/sapenc.c

@@ -140,6 +140,7 @@ static int sap_write_header(AVFormatContext *s)
         goto fail;
     }
 
+    if (s->start_time_realtime == 0  ||  s->start_time_realtime == AV_NOPTS_VALUE)
         s->start_time_realtime = av_gettime();
     for (i = 0; i < s->nb_streams; i++) {
         URLContext *fd;

libavformat/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFORMAT_VERSION_MAJOR 55
 #define LIBAVFORMAT_VERSION_MINOR 34
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \