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recompressing in sorenson

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Desrever
recompressing in sorenson
on Jun 13, 2007 at 10:55:05 pm

I've got several quicktime clips that a client wants recompressed in Sorenson to get the file size down. I know you're not supposed to compress already compressed footage but I don't have a choice in this situation. The problem is that any format I'm exporting, .wmv, QT, Real, the end video looks very choppy no matter what settings I've tried. I've tried various bitrates and resolutions, altering the frame rate ratio, 2passVBR to 1passCBR even streaming vs progressive but they all end up looking like they're playing at 5 fps.

any ideas?

original clips look like they're at 320x240, probably 25 or 30 fps


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Aharon Rabinowitz
Re: recompressing in sorenson
on Jun 20, 2007 at 4:56:10 am

Just a though but - if they were compressed using a combo of interval based keyframes (so like 1 every 10 seconds) and automatic keyframes (based on scene changes/difference in look) and there are a lot of keyframes at the end, perhaps it's causing an issue, when being read by squeeze.

does the very end of the video have fast moving or rapidly changing video?

This is complete conjecture, btw - I have no idea if this would cause a problem - but I do know that keyframes often cause a repetition of frames when decoded (played back). That migth explain why the video seems to play at a low frame rate. It may actually be playing at the right frame rate, but just showing repeated frames.

Try this - turn off automatic keyframes in squeeze (in the advanced settings) and see if that works.

Also do a frame by frame check of the original video and see what it looks like - is it distorted or repetative?


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Desrever
Re: recompressing in sorenson
on Jun 26, 2007 at 10:59:19 pm

In the end, I just ended up converting using Riverpast cleaner; but what you said makes sense about Squeeze having a tough time with different keyframes; I was thinking initially that it looked like a 24fps vid trying to play at 29.97fps (repeating keyframes like you mentioned). The video also had some time remapping, well, more of a strobe effect actually, so squeeze could have been having issues with that.
Thanks for the response Aharon


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