[vdr] Re: Playing DVD ?

[Andreas Schultz <aschultz@warp10.net>]

On Friday 29 August 2003 09:10, Axel Gruber wrote:

[...]

> A other thing: often i hear "the Error is the DVD because itīs structure is
> not DVD Conform" - i canīt understand this because most of other Player
> (also Software-Player for WIN) play this DVDīs correct and iīm sure they
> will not ask a VDR user to produce a "konform" DVD  :-)

There is a fundamental difference between all those software/hardware players 
and VDR: VDR uses a DVB card. People tend to forget that the av711x and the 
firmware where not designed for DVD but for DVB streams. There are things on 
commercial DVD's that are not DVD standard konform but are still resonably 
within the limits of the MPEG specification that a normal MPEG decoder can 
deal with them. The DVB card on the other hand is not so forgiving.

Some real-life examples:

1. audio/video latency

MPEG specification allows up to one second of audio/video latency. The DVB 
card, due to the limited buffer memory will produce significant distortions 
if the latency exceeds something around 300-400 ms or about 200kbyte worth of 
data (this is just a guess based on prior observation).

2. screwed audio/video PTS

Getting video and audio in sync is not easy. Early version of the dvd stuff 
had serious problems with that. The solution is to let the DVB card do the 
syncing. The syncing done by the card is based mostly on the PTS (presentaion 
time stamp). I have seen DVD's where the progress in  the PTS did not match 
the amount of data present. Basicly the PTS was increased at only half the 
speed of the audio stream. This will obviously screw audio/video sync big 
time.

3. PTS jumps

PTS might be reset (restarted) across chapter boundaries. They are guaranteed 
to jump during menu transitions. The DVB cards firmware handles those jumps 
very badly, resulting in short stutter when a chapter transition happens.


Some of the above problems can (and should) be worked around. Others require 
an amount of mpeg stream preprocessing that only an mpeg expert will be able 
to implement. Until you find such an expert or become one, you will have to 
accept those limitations.

Have fun

Andreas


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