[vdr] Fix for recording problem in VDR 1.7.20

Reinhard Nissl rnissl at gmx.de
Fri Sep 2 21:37:59 CEST 2011


Hi,

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)
> this
> 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".

Bye.
-- 
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rnissl at gmx.de



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