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Re: Using looped audio in a Quicktime movie

At 5:03 PM +0200 8/25/05, Jan E. Schotsman wrote: 
On 25-aug-05, at 15:50, Culann mac Cabe wrote:

Furthermore, if I can do the above in QT, how about having 2 similar audio
tracks playing independently such that a customised player, which I will
create using the QT API, could allow the user to interact with each,
allowing him/her to eg mute one track, raise the audio level of another
etc?...

You can use SetTrackVolume for this. SetTrackEnabled(false) mutes the track but restart of playback might be slower than setting the volume to 0.

SetTrackVolume() makes a persistent change in the track volume: when the movie is saved, the volume setting is saved with it. With QuickTime 7, we added APIs to make non-persistent track volume changes (ie, changes that affect playback but will not be saved):
SetTrackAudioGain()
SetTrackAudioMute()

There are also Track Properties (see QTSetTrackProperty ) that have identical effect:
kQTPropertyClass_Audio, kQTAudioPropertyID_Gain
kQTPropertyClass_Audio, kQTAudioPropertyID_Mute

If you are trying to mute/unmute the track dynamically, it is better to use SetTrackAudioMute rather than fiddling with the volume/gain.


How accurate can I hope sync to be: for musical re-mixing, it pretty much as
to be audio sample accurate - any issues here?

As long as audio tracks are all enabled (even if muted) when playback starts, QuickTime 7 should be playing them all with sample-accurate sync. While this is demonstrably true for uncompressed audio tracks, there may be some slight differences when tracks have been compressed into different audio formats.

Daniel Steinberg
QuickTime Engineering
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 >Re: Using looped audio in a Quicktime movie (From: "Jan E. Schotsman" <email@hidden>)



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