On May 22, 2006, at 2:56 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.
Not exactly what I asked. Setting the target OS in XCode to 10.2.8
causes my code to NOT compile.
I know what you are saying, but its not working.
Not sure, but I believe QT 7 required OS X 10.3 at least.
- 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.
I assume this means for EACH movie, I can have ONE session open,
thus making new movies allows me to have, effectively, many open.
This is what I need. I may be extracting data out of the SAME audio
track, but for each reference movie, at different times in the movie.
Yes, that's right.
- 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.
So, if the track in question is stereo, and all others are set to
"unused", then I just pick out the left or right track as needed.
Just pick out the left or right _channel_ as needed. I think that's
what you meant though.
Is there any other track layouts, like say 5.1 where I have more
options than just left and right PER TRACK?
I'm not sure I understand the question. QuickTime audio tracks now
allow any number of channels of audio, and those channels can be
labelled using any of the AudioChannelLabels supported by CoreAudio
(see CoreAudioTypes.h). You need to be prepared for strange things
-- for instance, you could have an audio track with 10 channels of
audio, each one labelled "Right". QTPro Users can relabel audio
channels at will in the Movie Jinfo window.
-Brad Ford
QuickTime Engineering
I'll try making the ref movie and will get back to you if there are
oddities.
Thanks again.
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