AE doesn’t like MP3’s any more than it likes other interframe compression schemes which, I suspect you may have.
Dave’s Stock Answer #1:
If the footage you imported into AE is any kind of the following — footage in an HDV acquisition codec, MPEG1, MPEG2, mp4, m2t, H.261 or H.264 — you need to convert it to a different codec.
These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.
In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.
Now, when you say the AVI is laggy, how are you trying to play it back? An AVI file that is uncompressed (especially an HD one) is NOT going to be able to be played off of a normal hard drive. The data rate is just too high. Try importing that AVI into Premiere and seeing if it plays back choppy.
Anyway, you should be using Premiere as your final output anyway. Export your lossless video (AVI or, Quicktime with a PNG codec [not a PNG sequence]) from AE and import it into Premiere (or straght into Adobe’s Media Encoder) and export it as your final file type, probably H.264 since you’re going to YouTube.
Again, one of Dave’s Stock Answers comes in handy:
Dave’s Stock Answer #3:
Don’t use AE to compress files for final delivery. The various compressors are there only to make quick ‘n dirty files showing a project’s progress to producers, clients, the kids, etc. AE is incapable of doing multipass encoding, a crucial feature that greatly improves the image quality of H.264 and MPEG-type files in particular.
Render a high-quality file from AE, and use a different application to do the compression. Popular ones are Adobe Media Encoder, Sorenson Squeeze and Apple’s Compressor, which comes bundled with Final Cut Suite. Even compressing in Quicktime Pro is better than compressing in AE.
Making good-looking compressed files is almost as much an art as it is a science. It is NOT straightforward at all. I recommend asking a few questions at the COW’s Compression Techniques forum.
As far as your audio goes, export it from Premiere as a WAV and use that in AE instead of the MP3 file.
The reason the “normal” MPEG-2 wouldn’t let you do 720 is that DVD’s can’t do HD. They’re stuck at the SD industry standard.
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