Re: Using the audio extraction API to extract to mixed mono?
Re: Using the audio extraction API to extract to mixed mono?
- Subject: Re: Using the audio extraction API to extract to mixed mono?
- From: William Stewart <email@hidden>
- Date: Fri, 3 Mar 2006 11:04:05 -0800
MovieAudio extraction is an API vended through QuickTime - I'd
suggest asking this question on the QT-API list.
Bill
On 03/03/2006, at 9:43 AM, Kaspar Fischer wrote:
Hi,
I need to extract the audio from a movie in such a way that
all present audio channels get mixed to a single one. I have
started with Apple's "demo" from
http://developer.apple.com/quicktime/audioextraction.html
but have run into a problem which is not covered there (and
the documentation has not helped me either). How can I set
the channel layout to "mono"?
Thanks,
Kaspar
P.S. My code so far is the following:
+ (OSStatus)extractAudioFromQPTMovie:(Movie)qtmov
withSamplingRate:(int)samplingRate
yieldingNumberOfSamples:(long *)actualSamples
{
OSStatus err = noErr;
MovieAudioExtractionRef extractionSessionRef = nil;
// begin extraction session:
signed char *tmp = nil;
err = MovieAudioExtractionBegin(qtmov, 0, &extractionSessionRef);
if (err != noErr)
goto bail;
// get the size of the extraction output layout:
AudioChannelLayout *layout = NULL;
UInt32 size = 0;
err = MovieAudioExtractionGetPropertyInfo(extractionSessionRef,
kQTPropertyClass_MovieAudioExtraction_Audio,
kQTMovieAudioExtractionAudioPropertyID_AudioChannelLayout,
NULL, &size, NULL);
if (err != noErr)
goto bail;
// allocate memory for the channel layout
layout = (AudioChannelLayout *) calloc(1, size);
if (layout == nil) {
err = memFullErr;
goto bail;
}
// get the layout for the current extraction configuration:
// (Note: this will have already been expanded into channel
descriptions.)
err = MovieAudioExtractionGetProperty(extractionSessionRef,
kQTPropertyClass_MovieAudioExtraction_Audio,
kQTMovieAudioExtractionAudioPropertyID_AudioChannelLayout,
size, layout, nil);
if (err != noErr)
goto bail;
// get the default audio extraction ASBD:
AudioStreamBasicDescription asbd;
err = MovieAudioExtractionGetProperty(extractionSessionRef,
kQTPropertyClass_MovieAudioExtraction_Audio,
kQTMovieAudioExtractionAudioPropertyID_AudioStreamBasicDescription,
sizeof(asbd), &asbd, nil);
if (err != noErr)
goto bail;
// convert the ASBD to return interleaved 8-bit PCM instead of
non-interleaved Float32.
asbd.mFormatFlags = kAudioFormatFlagIsSignedInteger |
kAudioFormatFlagIsPacked
| kAudioFormatFlagsNativeEndian;
asbd.mBitsPerChannel = sizeof(signed char) * 8;
asbd.mBytesPerFrame = 1; // sizeof(SInt16) * asbd.mChannelsPerFrame;
asbd.mBytesPerPacket = asbd.mBytesPerFrame;
asbd.mSampleRate = samplingRate;
asbd.mFramesPerPacket = 1;
asbd.mChannelsPerFrame = 1;
// set the new audio extraction ASBD:
err = MovieAudioExtractionSetProperty(extractionSessionRef,
kQTPropertyClass_MovieAudioExtraction_Audio,
kQTMovieAudioExtractionAudioPropertyID_AudioStreamBasicDescription,
sizeof (asbd), &asbd);
if (err != noErr)
goto bail;
// extract:
tmp = malloc(NROFSAMPLESPEREXTRACTIONCALL);
AudioBufferList bflst = {1, {{1, NROFSAMPLESPEREXTRACTIONCALL,
(void *)tmp}}};
UInt32 flags = 0, numFrames;
while ((flags & kQTMovieAudioExtractionComplete) == 0) {
numFrames = NROFSAMPLESPEREXTRACTIONCALL;
err = MovieAudioExtractionFillBuffer(extractionSessionRef,
&numFrames, &bflst, &flags);
if (err != noErr)
goto bail;
// processing:
NSLog(@"MAEFB returned %d frames", numFrames);
}
bail:
if (tmp != nil)
free(tmp);
return err;
}
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