On Mon, May 27, 2024 at 3:47 PM llyyr <llyyr.pub...@gmail.com> wrote: > > 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> > --- > libavformat/mpegts.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c > index c66a1ea6ede0..0d80ad80f1aa 100644 > --- a/libavformat/mpegts.c > +++ b/libavformat/mpegts.c > @@ -2944,6 +2944,12 @@ 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); > +
I think this doesn't work with mpegts_resync, since it always resyncs for the packet start to be on the 0x47 marker, not 4 bytes before it. So if sync is lost, it would never recover, if I read this right. - Hendrik _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
