[MPlayer-dev-eng] DVB-TS and ATSC-TS Differences

[James Courtier-Dutton]

Greg Herlein wrote:
> It's come to light in my work on transport streams this week that
> DVB-formatted streams (prevalent in Europe and on many satellites
> here in the US) have subtle differences from ATSC-formatted
> streams (prevalent here in the US for digital broadcasting,
> especially the free to air terrestial).
> 
> Specifically, the mapping of AC3 audio is done in 'PES private
> streams' in DVB where it's has a mandated stream type of 0x06.
> In ATSC it has to be set to a stream type of 0x81 and is a normal
> audio PES stream.
> 
> Reference:
> 
> http://www.atsc.org/standards/a_52a.pdf
> (see pages 118-127)
> 
> There must be other differences as well.  Does anyone know of a
> definitive paper or document that details all these?  If not, is
> anyone willing to help produce such a document?
> 
> Thanks!
> 
> Greg
> 
I have also done a lot of research on transport streams, and you are 
correct in your findings.
The most annoying problem I have found it identifying the contents of 
the private stream. As it can be AC3 audio or Subtitles/Teletext.
The start of a PES pack does not always match the start of an AC3 frame.
When using some cheap DVB cards, only the Video and Audio PID is 
received. The DVB card filters out the PAT and PMT, so the stream being 
played has lost descriptive information. If people have recorded that 
stream, and saved it to hard disc, that PAT/PMT information will be lost 
forever.
The only way of sorting out this problem I have found is for the demuxer 
to do AC3 based CRC checks to see if valid AC3 frames are arriving in 
this PID, and only then send the frames to the AC3 decoder. This does 
require the demuxer to do AC3 specific checks, but I find that it is the 
only reliable method for handling this.

Cheers
James