[mythtvnz] TVNZ DVB-S Playback issues due to variable GOP size

[Wade Maxfield]

Steven Ellis wrote:
> TVNZ made some changes to their DVB-S transmissions a couple of weeks ago,
> at which time they introduced variable GOP sizes into the MPEG2 streams.
> 
> On DVD MPEG2-PS streams have a maximum GOP size of 30. For MPEG2-TS
> streams over DVB you can exceed this value which can result in much better
> compression.
> 
> Since they made the change I've noticed that I get occasional playback
> issues on the TVNZ channels. This happens on both recordings and LiveTV.
> What appears to happen is the video might suddenly speed up and then slow
> down over the space of a second or so. Its like the MPEG2 decoder is
> confused on how to maintain sync between the audio and video due to the
> GOP length.
> 
> I'm normally using the "LibMPEG2" decoder with BOB deinterlacing, and I
> don't use "Video as the Timebase" as that can result in slightly fast
> audio.
> 
> Has anyone else noticed similar issues, and if not what video playback
> options are you using.
> 
> Steve

I've noticed something that may be exactly what you describe.  While 
watching the V8 Supercars on SportExtra I noticed a little bit of 
blurring on the ticker text, even though I was using Bob deinterlacing. 
  It would last a second or so then go back to super smooth scrolling 
and crisp text (as normal) then maybe repeat 20 or so seconds later. 
The cars themselves also slightly blurred about the same time.

I haven't noticed it during any other programs, but I don't watch much 
off One or TV2.

I'm using Standard MPEG2 playback, with Bob deinterlacing.  I did try 
LibMPEG2 for a little bit but ended up with a checkerboard like 
corruption for about a second immediately after doing a skip or when 
starting playback. Kind of like it's looking for a keyframe to 
synchronise the picture.

  - Wade