Re: Stream's format handle by the Siemens board and the VDR

[Marcus O.C. Metzler <mocm@netcologne.de>]

Klaus Schmidinger writes:
 > What I mean is the format which the new 0.7 driver delivers by default (PS_STREAM).
 > I was under the impression that this is what's generally referred to as MPEG2,
 > but I may be wrong. Anyway, VDR will the work with the data which the driver
 > delivers by default.
 > 
Ok, here is a little bit about MPEG2 and the different types of
streams:


1) Elementary stream (ES): is the stream that contains the actual compressed
                           audio and video data, like I, P, B-Frames
			   etc., with respective headers and some
			   other information.

2) PES Stream: (ok I forget what the acronym stands for, I`d have to
	       look it up) 
	       is composed of Packets containing ES data (so the P
	       probably stands for packetized). The packets have
	       headers, that specify the respective ES data, like
	       0x000001E0 for the first video stream. The header also
	       holds the packet length and stuff like the PTS. 

3) Program Stream (PS):	mainly contains PES packets with some
			additional packets containing some more
			information for the decoder, like the SCR,
			buffer sizes and mux rates. PSs are used by
			DVDs and distributed .vob files.

4) Transport Stream (TS): is composed of packets that all have the
			  same size (188k). They all start with 0x47.
			  The packets are identified by their PID.
			  Some of them contain audio and video data
			  in the form of PES packets which are spread
			  over many packets of size 188k. Other
			  packets contain sections which contain various
			  things like the PMT, the PAT or videotext
			  data. A TS is meant for transporting data
			  over networks. 

5) AV_PES: is the format used by the Siemens (Technotrend) DVB card internally.
	   The audio AV_PES packets contain audio PES packets with a
	   header that tells you wether there is a PTS in the
	   packet. The video packets are video PES packets without the
	   PES header (that really means the are ES streams) with a
	   header that may contain a PTS. The data originally comes
	   from a TS, but has already been processed by the decoder
	   and is read from the decoders buffer.

Of course the stuff up there is only to give you a little insight. If
you want to know more have a look at the av_pes2any sources in the
driver package, or at the MPEG2 specs.

The dvb driver can now read and write PES, PS, TS and of course
AV_PES. You have to remember that all the no AV_PES formats are
created from/reduced to AV_PES within the driver. There may still be
some errors in the conversion process. I can only say for sure that
the driver can correctly read the data that it wrote. For any other
decoders I would like to hear how it works. I tried the PS with the
Margi DVD-TO-GO PCMCIA card under Linux, but I haven`t got any other
ways to test it. I tried one of the software decoders for Win98, but I
forget the name (and I am not going to boot windoze just to look it
up). Anyway, it worked.


Marcus

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Dr. Marcus Metzler                             
mocm@netcologne.de                     http://www.metzlerbros.de
mocm@convergence.de                    http://www.convergence.de

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