Audio problems after compression

Posted by wilmagness 
Audio problems after compression
November 08, 2010 01:10PM
I am not sure if the problem is in Compressor or FCP.

First, using "Send to Compressor" I compressed a 1 hour sequence using the "DVD 90 Minutes Best Quality" settings creating an MPEG and a Dolby Digital file.

The video came out fine, but about half way through the sound file, the audio cuts out and there is complete silence for the rest of the file. I retried compressing a few times and got the same result.

I went through the FCP sequence and replaced a number of MP3 files with AIFs because I read that the embedded compression could cause problems, but this did not fix it.

I then exported the sound as an AIF from FCP and, using Compressor, tried to create the Dolby Digital file again. This time all of the audio is there, but around the same place there is a very loud crunchy/static/beeping sound that lasts about 30 seconds. The rest of the audio is fine.

The sequence I am working in has many audio tracks due to the fact that we overdubbed most of the movie and inserted tone and sound effects. Most of the files are AIFs, but some of them are WAVs. Could this be the problem?

Going through the whole movie and converting all of the files to AIFs and replacing them would be a huge project, so I'm not eager to do that. If anyone has any idea what may be causing this, I would be very interested.

I am using:

Compressor 3.5
On a 15" MacBook Pro
Re: Audio problems after compression
November 08, 2010 01:14PM
Do an audio mixdown before exporting. (Apple option R)
Re: Audio problems after compression
November 08, 2010 09:30PM
Okay, I just went into FCP, did an audio mixdown, sent to compressor and compressed to a Dolby Digital ac3 file.

Upon reviewing the file, about halfway through the audio cuts out and there is silence for the rest of the file. It happens about 8 minutes earlier than the last time I did it.

Is there anything else it might be?

Thanks so much for your help by the way!
Re: Audio problems after compression
November 08, 2010 09:38PM
Have you tried exporting a self-contained QuickTime movie and bringing that into Compressor instead of exporting directly from FCP?

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Re: Audio problems after compression
November 09, 2010 02:47PM
Yes, I tried exporting a self-contained movie with the same result.

I think I've resolved it, most likely the answer was far too rudimentary for anyone to think of. I had my sequence audio setting at 48 kHz while most of my audio was 44.1 kHz.

I switched the sequence setting, rendered again, and voila!

Thanks for the help everyone!
Re: Audio problems after compression
November 23, 2010 11:32AM
This only works because you are going to DVD. You would be pretty hosed with most other export formats. FCP is usually flakey with audio of different sample rates. Video (as well as FCP), likes audio to be 48khz, because it can more easily lock the audio in sync with the picture.
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