On May 22, 2006, at 2:38 PM, Steve Israelson wrote:
I have been experimenting with the new audio extraction API in QT.
I have some questions:
- What is the min version of OSX this works on. It does not seem to
compile on 10.2.8.
QT 7.0.
- How many audio extraction sessions can I have open on a movie?
Some other post suggested 1 only. If that is the case, then why is
this not documented a LOT better? Seems a very important restriction.
One at a time.
- Given the above, can I make a NEW movie referencing each audio
track I want data out of, and then start a new session on that movie?
Yes.
Or are these APIs going to follow the reference and decide that
there is already a converter for that?
- If the above fails to work, can I open and close the converter
after converting a few thousand samples, reconfigure it, and repeat
thus multiplexing how many sessions I want open by repeating this
open and close with each session I want? What kind of performance
hit will I take?
You could. But that would require doing a lot of setting the movie
time on the movie and jumping around, possibly resulting in seaming
problems. I would do the above approach.
- One other way... if I go into core audio directly, can I have
more conversion sessions open?
If you go CoreAudio directly, you're going to have to do all the
source audio track decompression and track mixing. It's a lot of
work, trust us.
- I want to extract and convert the audio from a single track. How
do I specify this? I can see how to specify left or right etc, but
that mixes all left and rights together, but I want say the left of
a single track only.
There are two ways.
1) iterate through the tracks in the source movie, get the track
layout, and set the channel labels you want to exclude to
kAudioChannelLabel_Unused. Note that if you leave, say, multiple
"Left's" labelled as "Left", they will still all mix into a single
"Left", unless you specify:
2) kQTMovieAudioExtractionMoviePropertyID_AllChannelsDiscrete on the
MovieAudioExtractionSession. This causes QuickTime to do _no_
mixing. You get all the source channels in all the audio tracks in
the movie (in order) if you set this property.
HTH.
-Brad Ford
QuickTime Engineering
That's all for now, thanks in advance if anyone has any answers...
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