Presently the mpegts demuxer passes the timestamps from received packets
directly to the output AVPackets. 2^33 / 90000
seconds is about 26.5 hours at which point applications start having a fit, and
that's assuming timestamps begin at time 0.
So here's a first revision of a patch to fix that issue.
Improvements possible:
* In its current form intended for continuous sources like over-the-air
receivers and multicast sources. When used on
files there will be problems with seeking.
* Constants such as 2^33 could be turned into macros for readability
>From d06a3bd39fc4f01b9ce6132d80634dd31be7b1aa Mon Sep 17 00:00:00 2001
From: DHE <g...@dehacked.net>
Date: Mon, 30 May 2016 18:31:43 -0400
Subject: [PATCH] libavformat/mpegts: Prevent wrapping of PTS & DTS
---
libavformat/mpegts.c | 56 ++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 48 insertions(+), 8 deletions(-)
diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index 7d78c41..a4d6bce 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -237,6 +237,10 @@ typedef struct PESContext {
int extended_stream_id;
uint8_t stream_id;
int64_t pts, dts;
+ /* for makings pts/dts consistent on long-running feeds */
+ int64_t last_dts;
+ unsigned int dts_wraps;
+
int64_t ts_packet_pos; /**< position of first TS packet of this PES packet */
uint8_t header[MAX_PES_HEADER_SIZE];
AVBufferRef *buffer;
@@ -341,6 +345,39 @@ static void set_pcr_pid(AVFormatContext *s, unsigned int programid, unsigned int
}
}
+static void fix_pts_dts(PESContext *pes) {
+ int64_t currdts;
+
+ if (pes->last_dts == AV_NOPTS_VALUE) {
+ pes->last_dts = pes->dts;
+ return;
+ }
+
+ // calculate the value we use for measurements against the last good value
+ currdts = pes->dts + (1ULL << 33) * pes->dts_wraps;
+
+ if (currdts < pes->last_dts) {
+ /* While wrapping backwards should never happen unless we overflow, bad
+ * input does happen. Don't wrap if the reverse in timestamps is small.
+ * I have selected 90000 (1 second) semi-arbitrarily.
+ */
+ if ((pes->last_dts - currdts) < 90000) {
+ pes->last_dts = currdts;
+ return;
+ }
+ currdts += 1ULL << 33;
+ pes->dts_wraps++;
+ av_log(pes->ts->stream, AV_LOG_INFO, "Stream timestamps wrapping\n");
+ }
+
+ pes->last_dts = pes->dts = currdts;
+
+ // Now fix the pts in the much the same way. It is always true that dts <= pts
+ pes->pts += (1ULL << 33) * pes->dts_wraps;
+ while (pes->pts < pes->dts)
+ pes->pts += 1ULL << 33;
+}
+
/**
* @brief discard_pid() decides if the pid is to be discarded according
* to caller's programs selection
@@ -1136,6 +1173,7 @@ skip:
pes->dts = ff_parse_pes_pts(r);
r += 5;
}
+ fix_pts_dts(pes);
pes->extended_stream_id = -1;
if (flags & 0x01) { /* PES extension */
pes_ext = *r++;
@@ -1268,14 +1306,16 @@ static PESContext *add_pes_stream(MpegTSContext *ts, int pid, int pcr_pid)
pes = av_mallocz(sizeof(PESContext));
if (!pes)
return 0;
- pes->ts = ts;
- pes->stream = ts->stream;
- pes->pid = pid;
- pes->pcr_pid = pcr_pid;
- pes->state = MPEGTS_SKIP;
- pes->pts = AV_NOPTS_VALUE;
- pes->dts = AV_NOPTS_VALUE;
- tss = mpegts_open_pes_filter(ts, pid, mpegts_push_data, pes);
+ pes->ts = ts;
+ pes->stream = ts->stream;
+ pes->pid = pid;
+ pes->pcr_pid = pcr_pid;
+ pes->state = MPEGTS_SKIP;
+ pes->pts = AV_NOPTS_VALUE;
+ pes->dts = AV_NOPTS_VALUE;
+ pes->last_dts = AV_NOPTS_VALUE;
+ pes->dts_wraps = 0;
+ tss = mpegts_open_pes_filter(ts, pid, mpegts_push_data, pes);
if (!tss) {
av_free(pes);
return 0;
--
1.8.4.1
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