[Ffmpeg-devel] [PATCH] generated PTS in MPEGTS wrong

Michael Niedermayer michaelni
Thu Mar 2 20:36:21 CET 2006


On Thu, Feb 23, 2006 at 10:55:58AM +0100, Alexander Kurpiers wrote:
> The current code in mpegtsenc.c tries to squeeze everything in PES
> packets of same size (DEFAULT_PES_PAYLOAD_SIZE), combining packets to
> always output complete packets. The PTS is included in every PES
> generated and is taken from the packets passed to mpegts_write_packet().
> This leads to wrong PES packets.
> The MPEG-2 system standard says ( Semantic definition of fields
> in PES packet ):
> "... In the case of video, if a PTS is present in a PES packet header it
> shall refer to the access unit containing the first picture start code
> that commences in this PES packet. A picture start code commences in PES
> packet if the first byte of the picture start code is present in the PES
> packet. "
> As there can be many picture start codes in the PES packet written, it
> is wrong to repeat the PTS on every packet, it is only valid for the
> first packet - that is the first bug. The second bug is that the PTS as
> delivered through pkt->pts belongs to the AVpacket passed. As the code
> in mpegts_write_packet() keeps filling up PES packets until they are
> "full", the new PTS is only written after the beginning of the AVpacket
> is already used up (to fill the last PES). So in general PTS information
> in the PES packets written lags by some bytes (the corresponding picture
> start code is not in the PES with the new PTS).
> My patch (attached) fixes the problem: the PTS is only written for the
> first PES packet and every delivered AVpacket starts a new PES packet. The
> drawback of this change is now that the length of generated PES packets
> is not constant anymore. If that is an issue, than I would see no
> alternative but to analyze the data and look for start codes (not nice...).
> I hope it helps. What I did not check (and what might be broken now) is the
> PCR though :-(

Mans Rullgard, you are listed as maintainer for mpegts* ...

if mans doesnt reply, then my oppionion is "rejected, the muxer should be
fixed similar to how we do mpeg-ps muxing, there is alot more then just
pts which must be correct"



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