ffmpeg | branch: master | llyyr <llyyr.pub...@gmail.com> | Mon May 27 19:10:31
2024 +0530| [550c662a1f94ddcd8d91f9874edc4b68d73fa7c7] | committer: Hendrik
Leppkes
avformat/mpegts: correctly skip TP_extra_header in m2ts
instead of just resyncing and skipping a bunch of TS packets, leading to
a loss of frames.
Before this, a stray byte with the value of 0x47 in TP_extra_header
would throw off the detection of where TS packets start.
A typical file that could cause issues would look like this:
00000300: 238f 4780 4750 1110 0000 01e0 0000 84c0
^^ ^^
The first four bytes here are TP_extra_header and the actual TS packet
starts at offset 0x304
FFmpeg would try to read a packet at 0x300 but since nothing skips the
4 byte TP_extra_header, find that the first byte is not 0x47 and
immediately go into mpegts_resync, and incorrectly detect the stray 0x47
in the TP_extra_header at 0x302 as the new sync byte.
Fix this by correctly skipping the first 4 bytes if the source packet
is 192 bytes.
Signed-off-by: llyyr <llyyr.pub...@gmail.com>
Signed-off-by: Hendrik Leppkes <h.lepp...@gmail.com>
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=550c662a1f94ddcd8d91f9874edc4b68d73fa7c7
---
libavformat/mpegts.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index 10589f798b..765bedec5c 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -2961,6 +2961,12 @@ static int read_packet(AVFormatContext *s, uint8_t *buf,
int raw_packet_size,
AVIOContext *pb = s->pb;
int len;
+ // 192 bytes source packet that start with a 4 bytes TP_extra_header
+ // followed by 188 bytes of TS packet. The sync byte is at offset 4, so
skip
+ // the first 4 bytes otherwise we'll end up syncing to the wrong packet.
+ if (raw_packet_size == TS_DVHS_PACKET_SIZE)
+ avio_skip(pb, 4);
+
for (;;) {
len = ffio_read_indirect(pb, buf, TS_PACKET_SIZE, data);
if (len != TS_PACKET_SIZE)
@@ -2983,7 +2989,11 @@ static int read_packet(AVFormatContext *s, uint8_t *buf,
int raw_packet_size,
static void finished_reading_packet(AVFormatContext *s, int raw_packet_size)
{
AVIOContext *pb = s->pb;
- int skip = raw_packet_size - TS_PACKET_SIZE;
+ int skip;
+ if (raw_packet_size == TS_DVHS_PACKET_SIZE)
+ skip = raw_packet_size - TS_DVHS_PACKET_SIZE;
+ else
+ skip = raw_packet_size - TS_PACKET_SIZE;
if (skip > 0)
avio_skip(pb, skip);
}
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