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Re: Audio extraction miss understand

Subject: Re: Audio extraction miss understand
From: Daniel Steinberg <email@hidden>
Date: Thu, 28 Sep 2006 10:20:17 -0700
Delivered-to: email@hidden
Delivered-to: email@hidden

Title: Re: Audio extraction miss understand

Siegfried:

In order to configure an Audio Extraction Session to extract discrete channels from the movie without mixing, you must set the AllChannelsDiscrete property on the session. What you have done below is to establish a destination channel layout that contains no active channels, which, if it worked, would have resulted in silence. You also hadn't set the extraction ASBD to match your channel layout, which is probably why it failed.

Anyway, you will have more luck if you do this:

Boolean allDiscrete = true;

Error = MovieAudioExtractionSetProperty(m_ExtractionSession,

kQTPropertyClass_MovieAudioExtraction_Movie,

kQTMovieAudioExtractionMoviePropertyID_AllChannelsDiscrete,

sizeof (Boolean), &allDiscrete);

You should then *Get* the kQTMovieAudioExtractionAudioPropertyID_AudioStreamBasicDescription property in order to determine how many channels this discrete extraction will return, so you can allocate your pull buffers appropriately.

Daniel Steinberg

QuickTime Engineering

At 6:49 PM +0200 9/28/06, Siegfried Hand wrote:

Content-class: urn:content-classes:message
Content-Type: multipart/alternative;
boundary="----_=_NextPart_001_01C6E31E.15C28936"

Hello, i think i have missed something in the audio extraction api.

I need to extract each audio track in each audio stream of a movie, to place them in a time line for editing

For ex a movie with two audio stream in it, one with a stereo track, and an other with a stereo track too.

So for my application i need to extract 4 mono tracks.

The audio extraction failed (-50) with this configuration (i have changed the asbd, layout properties & set the mixing as discreet)

But if i edit the movie in quicktime 7 (i leave the first stream as it was (left and right), i set the left channel of the second stream as center-left and the right channel of the second stream at center-right)

The result is L CL CR R and there everything is fine

So i think i missed something about discreet channel mixing & the channel layout.

Here is tha way i set the channel layout :

UInt32 size = fieldOffset(AudioChannelLayout, mChannelDescriptions[m_Asbd.mChannelsPerFrame]);

AudioChannelLayout* playout = (QT::AudioChannelLayout*) calloc(1, size);

// expand the layout into a full layout using channel descriptions:

size = sizeof(AudioChannelLayout);

playout->mChannelLayoutTag = kAudioChannelLayoutTag_UseChannelDescriptions;

playout->mNumberChannelDescriptions = m_Asbd.mChannelsPerFrame;

for (int i = 0; i < m_Asbd.mChannelsPerFrame; i++)

{

playout->mChannelDescriptions[i].mChannelLabel = kAudioChannelLabel_Unused;

}

Error = MovieAudioExtractionSetProperty(m_ExtractionSession, kQTPropertyClass_MovieAudioExtraction_Audio, kQTMovieAudioExtractionAudioPropertyID_AudioChannelLayout, size, &playout);

If somone can help me to clarify this point.

Thanks.

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References:
	>Audio extraction miss understand (From: "Siegfried Hand" <email@hidden>)

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