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tsdemux: Handle "negative" timestamps

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This is only enabled in push time mode. Furthermore it's only enabled for now if
PCR is to be ignored.

The problem is dealing with streams where the initial PTS/DTS observation might
be greater than following ones (from other PID for example). Before this patch,
this would result in sending buffers without any timestamp which would cause a
wide variety of issues.

Instead, pad segment and buffer timestamps with an extra
value (packetizer->extra_shift, default to 2s), to ensure that we can get valid
timestamps on outgoing buffers (even if that means they are before the segment
start).

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1179>
This commit is contained in:
Edward Hervey 2021-09-05 11:57:18 +02:00 committed by GStreamer Marge Bot
parent 74e9d44db3
commit 0ff569d408
3 changed files with 16 additions and 1 deletions
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3
subprojects/gst-plugins-bad/gst/mpegtsdemux/mpegtspacketizer.c
View file

@ -285,6 +285,7 @@ mpegts_packetizer_init (MpegTSPacketizer2 * packetizer)
packetizer->pcr_discont_threshold = GST_SECOND;
packetizer->last_pts = GST_CLOCK_TIME_NONE;
packetizer->last_dts = GST_CLOCK_TIME_NONE;
packetizer->extra_shift = 0;
}
static void
@ -2277,7 +2278,7 @@ mpegts_packetizer_pts_to_ts (MpegTSPacketizer2 * packetizer,
GST_TIME_ARGS (pcrtable->base_pcrtime),
GST_TIME_ARGS (pcrtable->base_time),
GST_TIME_ARGS (pcrtable->pcroffset));
res = pts + pcrtable->pcroffset;
res = pts + pcrtable->pcroffset + packetizer->extra_shift;
/* Don't return anything if we differ too much against last seen PCR */
if (G_UNLIKELY (pcr_pid != 0x1fff &&

4
subprojects/gst-plugins-bad/gst/mpegtsdemux/mpegtspacketizer.h
View file

@ -287,6 +287,10 @@ struct _MpegTSPacketizer2 {
/* PTS/DTS of last buffer */
GstClockTime last_pts;
GstClockTime last_dts;
/* Extra time offset to handle values before initial PCR.
* This will be added to all converted timestamps */
GstClockTime extra_shift;
};
struct _MpegTSPacketizer2Class {

10
subprojects/gst-plugins-bad/gst/mpegtsdemux/tsdemux.c
View file

@ -1051,6 +1051,16 @@ push_event (MpegTSBase * base, GstEvent * event)
gboolean early_ret = FALSE;
if (GST_EVENT_TYPE (event) == GST_EVENT_SEGMENT) {
if (base->segment.format == GST_FORMAT_TIME && base->ignore_pcr) {
/* Shift start/stop values by 2s */
base->packetizer->extra_shift = 2 * GST_SECOND;
if (GST_CLOCK_TIME_IS_VALID (base->segment.start))
base->segment.start += 2 * GST_SECOND;
if (GST_CLOCK_TIME_IS_VALID (base->segment.stop))
base->segment.stop += 2 * GST_SECOND;
if (GST_CLOCK_TIME_IS_VALID (base->segment.position))
base->segment.position += 2 * GST_SECOND;
}
GST_DEBUG_OBJECT (base, "Ignoring segment event (recreated later)");
gst_event_unref (event);
return TRUE;