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Compression when authoring DVDs

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Compression when authoring DVDs
on Nov 22, 2007 at 2:31:47 pm

I am having some trouble authoring onto DVD (using Sony DVD Architect 3.0).
I have a DV-AVI original file which is roughly 2.5GB (which should obviously easily fit onto a DVD) to start with, but when I author the DVD through architect (I want to add a menu) it compresses down to roughly 700MB. When I go into the 'optimise DVD' table, it says the film will fit on the disk without neding to be compressed, but when I burn the DVD it comes up with a warning that it will be.
I understand that some compression will be needed in the encoding, but this much?! I must admit I don't fully understand DVD compression, but is there no way I can finish with a 2-2.5 GB disk which has as little a compressed version of the film as possible?
On top of this the file is already compressed from an HDV project, so the extra compression is painfully noticable.
Anyone have any thoughts?
Much appreciated,

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Ed Dooley
Re: Compression when authoring DVDs
on Nov 22, 2007 at 3:12:38 pm

Well, the main thing is that AVI is not a supported DVD format. DVDs use MPEG-2 compression. The best thing, if possible, is to start with the original edited video and compress directly to MPEG-2 to author from. If you can't do that, you will have to re-compress it.
DVD players have a sweet spot as to how high a data rate they'll be able to play withing skipping/dropping frames. Although the official spec for maximum data rate (I think) is 9.8Mbps (or close to that), a lot of players will skip long before that rate. There are a lot of recommendations about the right rate, but somewhere in the 5 to 7Mbps is good. If you max out at 7Mbps for your already compressed file, it will give you the best you can get from what you started with.

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