Wednesday, May 23, 2007

audio sync, nudge, avidemux2 and a reminder about archiving

I spent most of the night trying to debug an audio synchronization problem in Cinelerra. The video was trailing the audio by a little bit. So I used the Nudge feature to slide the audio .5 seconds behind to the right.

A word about nudge:
If the audio is running behind the video, use POSITIVE values for nudge.
If the video is running behind the audio, use NEGATIVE values for nudge.

Another way to put it:
If your audio is lagging and is behind the video (more to the RIGHT on the timeline than the video), push it FORWARD using positive values.
If your audio is running too fast and is ahead of the video (more to the LEFT on the timeline than the video), push it BACKWARD using negative values.

Since nudge is good for fixing an entire track, one way to fix synchronization problems that occur on only part of a track is to use the Delay Video video effect or the Delay Audio audio effect:
  • The Delay Video track works when audio lags behind the video.
  • The Delay Audio track works when the video lags behind the audio.
The two effects take positive values for the delay in seconds. So they only work "one way", so to speak.

This syncronization problem was after another discovery that Cinelerra on the Fedora Core 6 box I just built is not letting me drag and drop video. So I couldn't manually slide my video around. I'm not sure why this is not working for this particular project, as the Record button is enabled and my editing Preferences seem correct. The funny thing is that it does not happen when I create a new project. My gut feeling is that this version of Cinelerra I am using is SLIGHTLY newer than the one on my main box. So the XML is probably screwed up in some way. Ugh. Tiring.

But not tired enough to write a reminder to everybody that if they want the MOST PORTABLE video files, keep them below 4GB. That way they will fit on a DVD for archiving or transferring, fit on a FAT32 file system and be welcomed on any modern file system. Any larger, and it becomes a nightmare to transfer or archive. As I edit in HDV, file sizes get huge pretty quickly. But keep 'em below 4GB kids! It'll save you much pain in the long run.

Your friend in the battle to trim files down to size is AVIDEMUX2, a wonderful little program I've mentioned before that chops up large video files in no time flat. On my system, a Dell 400SC, 3.2Ghz, 2GB RAM, multiple drives, it took about four minutes total to chop up a 5GB HDV file into two 2.5 chunks. Not bad! One thing I do is to make sure that when you are saving out your file, use Copy for both the Audio and Video tracks and then save to your final format. The Copy feature will save out a new file to the exact same specs as your source file. Very nice feature!

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