When I export AIFF audio from an FCP7 project, the resulting file is always slightly shorter than the original, thus slightly out of synch. Same thing happens if I use Compressor to extract the AIFF file. (I need to export the AIFF in order to get rid of a hum.)
Is there a way to get round this?
Thanks.
iMac, OS X Mountain Lion (10.8.2)
iMac, OS X Mountain Lion (10.8.2)
Is your original source audio 48k 16 bit? and do your sequence settings match your audio? If not, this may be the source of your problem.
Yes, 48k 16bit. Both vid and audio are extracted from a PAL dvd, uncompressed. Vid sequence settings match those of the original dvd. There are no sequence settings for audio. When vid and audio are exported together as a .mov file, everything is in synch; ditto when compressed to m2v and ac3.
But if at any point the audio is extracted separately (direct from FCP; from the .mov file; from uncompressing the ac3) the resulting file is a few seconds shorter than the vid file.
The reason for exporting is to remove hum from the audio. (I don't know if I can do this, by sampling, within FCP.)
The only solution I've found is to increase the duration of the audio (i.e., slow it down slightly).
Not sure I understand. How did you extract the files from the dvd? Generally speaking, MPEG Streamclip does a great job (as long as the dvd is not copy protected). Did you convert to a quicktime? What do you mean there are no sequence settings for audio? If there's audio in your sequence (which there seems to be), there are settings for the audio.
The only thing I can suggest is before bringing the files into fcp, make sure that the easy setup frame rate matches the source and sequence (I assume that's 25 fps). Every once in a while, you can have issues importing audio when there's a mismatch between your sequence and your easy setup frame rates. Never seen this with exporting.
The vid and audio are extracted as a single .mov file, which then is put into FCP. At this point, audio and vid match perfectly. And, if I export the sequence as s single .mov file, again audio and vid match perfectly.
It's only when I export the audio separately that it goes out of synch -- either exported as Audio to aif, or, after exporting a .mov file (again in synch), if I subsequently use Compressior some other program to extract the audio from the .mov file.
Yes. Sequence settings match those of the original .mov. There are no separate sequence settings for audio -- both audio and vid are part of the same sequence. And yes, audio is 48k, 16bit.
what compressor (or codec) is the file and what is the compressor for the sequence?
You can use Compressor simply to extract the audio (as aiff) from a mov file. So no compressing or uncompressing is taking place. The result is shorter than the .mov file.
As I said, if I export audio directly from FCP's sequence I get a shorter file. If I export the whole mov sequence and afterward extract the audio (using Compressor), the result is an identically shorter file.
Also, if I take ,mov file and import it into an audio program (like Audacity or Amadeus), it extracts the audio once again as an identically shorter file. Which is impossible, since it's not shorter within the actual mov file!
The only chance we have of figuring out what's going on is if we approach this in a systematic way and you answer the questions completely.
I don't think you understand what a codec or compressor is in this context. Even an uncompressed file has a codec or compressor. It's just the standard with which the digital information is organized (at least that's the way I understand it). If you select your source clip in the browser or the timeline and hit command-9, you'll see the clip settings and you'll see the compressor or codec. If you make the timeline active or select it in the browser and hit command-zero, you'll get your sequence settings and you'll see the compressor or codec.
Also, just to make sure, is your source clip frame rate and sequence setting frame rate 25 fps?
Command-9 for vid: 25fps. 720x576. Compressor: None. Data rate 29.8MB/sec. Pixel: PAL - CCIR 601.
Command-9 for audio: (no fps given). Data rate 29.7 MB/sec. 48K. 15 bit integer.
Sequence settings: 720x576. CCIR 601/ DV PAL (5:4). Field: upper. Editing timebase 25. Copressor: none. Audio: rate: 48k, 15 bit. Channel Grouped.
I can't find the word "codec" anywhere.
To repeat: the above settings are identical for an exported .mov file from FCP (it's uncompressed).
And they were the same for the mov file before it came into FCP.
As I said, the files were originally extracted from the dvd at "Apple FCP Uncompressed 8-bit 4:2:2." (48k audio) Maybe this is what you mean by a codec, though I can't find that word anywhere (but I'm far from being expert).
And that's what I get when I export the sequence as mov file from FCP itself.
Didn't realize this was possible and it is way overkill for ripping a dvd and may be the problem. DVD's are heavily compressed and ripping to prores is more than sufficient to maintain whatever quality remains. Certainly worth a shot to see if it solves the problem.
FCP exporting aiff problem
