[vdr] Fix for recording problem in VDR 1.7.20
rnissl at gmx.de
Fri Sep 2 21:37:59 CEST 2011
Am 02.09.2011 16:08, schrieb Klaus Schmidinger:
> Apparently in this file every TS packet that starts a new PES packet
> has the "Payload Unit Start Indicator" flag set. Normally (AFAIK)
> should only be set for TS packets that contain the beginning of an
> actual payload unit (which may consist of several PES packets).
> So I would assume that the TS data is in error.
I don't think that this assumption is correct. The playload start
is related to carried payload only, i. e. PES packets in case of
the video stream. And it would be sufficient to put there just a
single byte of the PES packet to set this bit, i. e. the first
0x00 of the start code sequence 0x00, 0x00, 0x01. Furthermore it
is specified that no second PES packet is allowed to start in the
same TS packet.
The PES layer itself has no access unit (= e. g. image) start
indicator. But when a PTS is part of the PES header, it has to be
applied to the first access unit (= e. g. image) which starts in
that PES packet (once again, it would be sufficient to put there
just the first byte of the start code sequence at the tail of the
PES packet). So you may use the PTS flag as Access Unit Start
Indicator ("AUSI"), which tells you that this PES packet will
start a new image but you cannot tell where, i. e. it is likely
that the PES packet will carry the tail of the previous image in
front of the new image. Using the "AUSI" is only of hint quality
as not every access unit (= e. g. image) will have a PTS
attached. Some stations label only I frames while others label
every frame or field.
In video streams, it is common use to have PES packets with a
zero length indicator which means the TS layer has to tell you
where the next PES packet starts. So such streams are likely to
have just a single PES packet per access unit (= e. g. image) and
as a result you see the TS PUSI at the same time as the PES "AUSI".
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rnissl at gmx.de
More information about the vdr