[mythtv] [PATCH] more pcHDTV channel-change improvements

[Doug Larrick]

On 2003.10.27 12:03, Jason Hoos wrote:
> I've looked into the problem a little bit with some printf-debugging  
> on hdtvreceiver.cpp, and it appears that the code is never finding  
> the GOP frames from this station.  I put printf's in the  
> FindKeyframes method inside the "// picture_start" and "//  
> group_of_pictures" if statments;  when it runs I get lots of  
> "picture_start" messages, but no "group of pictures" messages.

Did you ever get any entries in your database's recordedmarkup table  
for these recordings?  If not, you were never seeing GOP_start frames  
to begin with, only now we care a lot more.  I suppose you could put in  
a timer... if we don't find GOP after some number of picture_start  
packets (which are frames, so 30 might be a good number), start sending  
data anyway.  You probably want to start at a picture_start frame in  
any case.

>  Or can anyone point me at a good reference for what the MPEG video  
> inside of an ATSC stream should look like so I can pick one apart and  
> see what's missing or why the GOP frames aren't being
> found?  (I do know about the TS format docs at www.atsc.org, but I
> didn't see anything there about how the video itself should be  
> formatted...)

Unfortnately the MPEG committee wants real money for the MPEG2  
standard.  This fact is also reflected in the price of the available  
MPEG2 books.  I suggest you look at the code in ffmpeg (libavformat/ 
libavcodec), Brent Beyeler's bbinfo/bbmpeg (do a Google search), and  
the example programs that come with the pcHDTV card.  Also do Google  
searches, especially on specific terms (like GOP or group.of.pictures)  
that you come across.  The ATSC docs have a high-level overview but are  
short on details.

-Doug