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Io HD, ProRes from Digital Betacam and sound longer than video

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Vladimir Novikov
Io HD, ProRes from Digital Betacam and sound longer than video
on Dec 7, 2012 at 10:26:06 pm

HI all,

I need to send the video with visible time code and VI sound overseas for dubbing, and I get a small problem while ingesting the DigiBeta using Io HD.

I use Mac OS X 10.8.2, last versions of Aja drivers and software and Compressor 4.0.6.

The Digital Betacam is acquired as ProRes 422HQ SD PAL QuickTime MOV file. When I check the movie properties (Command - J), I see the video track 1:02:30:04 long and four sound tracks 1:02:30:21 long.

So, the sound tracks are a little bit longer then the video track. I didn't notice any problem of video/audio sync, but still...

I've used Compressor to produce an h.264 file with visible time code and the file has both streams 1:02:30:04 long.

Now, when I export the sound using the Export -> Sound to AIFF command, I get two possibilities: one AIFF file with two discrete channels or one AIFF file with a stereo pair. In both cases the file is 1:02:30:04 long, so Quicktime corrects this small difference of duration.

But if I use the Extract option from the properties view, I get two independent AIFFs each 1:02:30:21 long.

I presume it's not a big deal, but still would like to know why it happens.

Other question, the dubbing guys ask me to send them the files as FLAC. I presume they want to save upload/download time and bandwidth, but I'm afraid another transformation will produce another time shift. FLAC and ALAC are lossless, so AIFF - FLAC - AIFF should in theory produce exactly the same file, but who knows...

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