To G.O.P. or not to G.O.P.

rjgeisler · Post by **rjgeisler** » Sat Jan 01, 2005 4:33 pm

ATI MMC has the option to turn GOP (group of pictures) ON/OFF in the frame sequence settings.

Should it be on or off? Does VStudio 8 care?

jchunter_2 · Post by **jchunter_2** » Sat Jan 01, 2005 4:41 pm

I would turn it on because the GOP is the basis of the Mpeg compression algorithm. If it is turned off, my guess is that every frame would be an "I" frame, causing mpeg files to be huge.

rjgeisler · Post by **rjgeisler** » Sat Jan 01, 2005 9:52 pm

That does not appear to be the case!

On or off, file sizes are about the same. Still have IBP frames! Older versions of ATI MMC did not have this option, Unless that was the default.

I don't see that it matters in UVS unless it somehow affects the Audio sync!

THoff · Post by **THoff** » Sat Jan 01, 2005 11:00 pm

rjgeisler wrote:I don't see that it matters in UVS unless it somehow affects the Audio sync!

It very well could, because when a GOP is closed, the timecode is inserted. If a decoder for either playback or transcoding relies on that to try to keep audio and video in sync to correct for small drifts (which often occur with analog captures), then you will see a progressive synch problem.

rjgeisler · Post by **rjgeisler** » Sun Jan 02, 2005 3:11 am

Thanks, That makes perfect sense!