GOP open or closed

looking for tips on the diffrence between these and what are the pros and cons of these two . tips and suggestion are welcome plz. how to treat KEYed PAL footage before exporting to compressor for NTSC Dvd . TIA.



thanks for those who SHARE-gev

A closed gop is one which does not rely on other gops around it for information - it stands on its own as a piece of footage and is entirely self-contained. An open gop *does* refer to frames from gops before and after itself. In so doing it works slightly more efficiently and results in a smaller file size when compressing.

Closed gops are pretty useful if you are doing multi or mixed angle work.

When going from PAL to NTSC you really want to look at doing a proper standards conversion, using one of the various pieces of software that handle it intelligently. Graham Nattress has a set of filters for FCP that get good results, but you could also look at using something like Canopus Procoder on a PC, or MegaPEG.X on your Mac.

I've not used Compressor to do a standards conversion since I first attempted it in V1. I didn't much care for the output from that, but I'd be interested to hear from others who have done it and find it OK.

thanks for the reply. we dont have multiple angle. it is pal footage ( 25p) turned to NTSC MEPG2 via compressor ( maybe we can do with nattress too) . for this KIND which u suggest . open or closed. in doing so anyother setting to MIND under GOP. Thanks



thanks for those who SHARE-gev

For efficiency, keep it open and make the GOP length 15 for the NTSC footage. This is pretty much the default setting and should work fine for you.

"I've not used Compressor to do a standards conversion since I first attempted it in V1. I didn't much care for the output from that, but I'd be interested to hear from others who have done it and find it OK".

Hey Hal.
It was recently discussed in Cafe LA.
The motion compensated/optical flow based standards conversion quality in Compressor 2 is probably beyond any other software tool. It doesn't do just standars conversion but it can't go from interlaced to progresive or viceversa and even upsamle SD to HD like nothing I've seen before.

Unfortunately, the processing times are also above any other software tool, making it unusable for anything but very short elements. If you enable the motion compensated (optical flow) frame rate convertion options, you will have around one minute of encoding time for one second of video, on a Dual G5!



Compressor 1 is not a reference for this matter, because it wasn't supposed to do standards conversion. Compressor 2 has a very sophisticated technology for this, but takes ages. Actually, it has a frame blending based conversion method which should be much faster, but I didn't try it. It's the technology most transcoding tools use, ie, not really great.



Adolfo Rozenfeld
Buenos Aires - Argentina
www.adolforozenfeld.com

Thanks for that Adolfo - I really ought to play with Compressor more. I do have a bank of G4s (and a couple of G5s now) at work which are largely unused, so I could try running Compressor over a group and seeing what impact that has on rendering this kind of thing.

What you say is enough to encourage me to try it, so I guess next week I'll be setting it up!

I am/was very happy with the standards conversion from Procoder, but then again I don't need to do a lot of that kind of work (last time was over a year ago now). It's about time I investigated alternatives... :-)

Hal: To tell you how important this is for me, let me say I live in a country where PAL is the standard for video/tv production, but NTSC is the defacto standard for DVDs! About 99 per cent of the stuff has to be converted. Imagine how painful is that



Adolfo Rozenfeld
Buenos Aires - Argentina
www.adolforozenfeld.com