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mpegtspacketizer: Better detect PCR resets

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Assume that any differences in PCR greater than 15s means there is
a reset in the stream.
This commit is contained in:
Edward Hervey 2012-07-19 13:35:51 +02:00
parent 508e4e7e9f
commit 121aa3ad13
1 changed files with 52 additions and 20 deletions
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72
gst/mpegtsdemux/mpegtspacketizer.c
View file

@ -193,7 +193,9 @@ typedef struct _MpegTSPCR
gint64 window_min;
gint64 skew;
gint64 prev_send_diff;
gint wrap_count;
/* Offset to apply to PCR to handle wraparounds */
guint64 pcroffset;
/* Used for bitrate calculation */
/* FIXME : Replace this later on with a balanced tree or sequence */
@ -281,7 +283,7 @@ get_pcr_table (MpegTSPacketizer2 * packetizer, guint16 pid)
res->skew = 0;
res->prev_send_diff = GST_CLOCK_TIME_NONE;
res->prev_out_time = GST_CLOCK_TIME_NONE;
res->wrap_count = 0;
res->pcroffset = 0;
}
return res;
@ -3352,8 +3354,7 @@ calculate_skew (MpegTSPCR * pcr, guint64 pcrtime, GstClockTime time)
GstClockTime gstpcrtime, out_time;
guint64 slope;
gstpcrtime =
PCRTIME_TO_GSTTIME (pcrtime) + pcr->wrap_count * PCR_GST_MAX_VALUE;
gstpcrtime = PCRTIME_TO_GSTTIME (pcrtime) + pcr->pcroffset;
/* first time, lock on to time and gstpcrtime */
if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (pcr->base_time))) {
@ -3369,22 +3370,51 @@ calculate_skew (MpegTSPCR * pcr, guint64 pcrtime, GstClockTime time)
GST_TIME_ARGS (gstpcrtime));
}
if (G_LIKELY (gstpcrtime >= pcr->base_pcrtime))
/* Handle PCR wraparound and resets */
if (GST_CLOCK_TIME_IS_VALID (pcr->last_pcrtime) &&
gstpcrtime < pcr->last_pcrtime) {
if (pcr->last_pcrtime - gstpcrtime > PCR_GST_MAX_VALUE / 2) {
/* PCR wraparound */
GST_DEBUG ("PCR wrap");
pcr->pcroffset += PCR_GST_MAX_VALUE;
gstpcrtime = PCRTIME_TO_GSTTIME (pcrtime) + pcr->pcroffset;
send_diff = gstpcrtime - pcr->base_pcrtime;
} else if (GST_CLOCK_TIME_IS_VALID (time)
&& pcr->last_pcrtime - gstpcrtime > 15 * GST_SECOND) {
/* Assume a reset */
GST_DEBUG ("PCR reset");
/* Calculate PCR we would have expected for the given input time,
* essentially applying the reverse correction process
*
* We want to find the PCR offset to apply
* pcroffset = (corrected) gstpcrtime - (received) gstpcrtime
*
* send_diff = (corrected) gstpcrtime - pcr->base_pcrtime
* recv_diff = time - pcr->base_time
* out_time = pcr->base_time + send_diff
*
* We are assuming that send_diff == recv_diff
* (corrected) gstpcrtime - pcr->base_pcrtime = time - pcr->base_time
* Giving us:
* (corrected) gstpcrtime = time - pcr->base_time + pcr->base_pcrtime
*
* And therefore:
* pcroffset = time - pcr->base_time + pcr->base_pcrtime - (received) gstpcrtime
**/
pcr->pcroffset += time - pcr->base_time + pcr->base_pcrtime - gstpcrtime;
gstpcrtime = PCRTIME_TO_GSTTIME (pcrtime) + pcr->pcroffset;
send_diff = gstpcrtime - pcr->base_pcrtime;
GST_DEBUG ("Introduced offset is now %" GST_TIME_FORMAT
" corrected pcr time %" GST_TIME_FORMAT,
GST_TIME_ARGS (pcr->pcroffset), GST_TIME_ARGS (gstpcrtime));
} else {
GST_WARNING ("backward timestamps at server but no timestamps");
send_diff = 0;
/* at least try to get a new timestamp.. */
pcr->base_time = GST_CLOCK_TIME_NONE;
}
} else
send_diff = gstpcrtime - pcr->base_pcrtime;
else if (GST_CLOCK_TIME_IS_VALID (time)
&& (pcr->last_pcrtime - gstpcrtime > PCR_GST_MAX_VALUE / 2)) {
/* Detect wraparounds */
GST_DEBUG ("PCR wrap");
pcr->wrap_count++;
gstpcrtime =
PCRTIME_TO_GSTTIME (pcrtime) + pcr->wrap_count * PCR_GST_MAX_VALUE;
send_diff = gstpcrtime - pcr->base_pcrtime;
} else {
GST_WARNING ("backward timestamps at server but no timestamps");
send_diff = 0;
/* at least try to get a new timestamp.. */
pcr->base_time = GST_CLOCK_TIME_NONE;
}
GST_DEBUG ("gstpcr %" GST_TIME_FORMAT ", buftime %" GST_TIME_FORMAT ", base %"
GST_TIME_FORMAT ", send_diff %" GST_TIME_FORMAT,
@ -3626,7 +3656,9 @@ mpegts_packetizer_pts_to_ts (MpegTSPacketizer2 * packetizer, GstClockTime pts,
GST_DEBUG ("pts %" G_GUINT64_FORMAT " base_pcrtime:%" G_GUINT64_FORMAT
" base_time:%" GST_TIME_FORMAT, pts, pcrtable->base_pcrtime,
GST_TIME_ARGS (pcrtable->base_time));
res = pts - pcrtable->base_pcrtime + pcrtable->base_time + pcrtable->skew;
res =
pts + pcrtable->pcroffset - pcrtable->base_pcrtime +
pcrtable->base_time + pcrtable->skew;
} else
/* If not, use pcr observations */
if (packetizer->calculate_offset && pcrtable->first_pcr != -1) {