Re: Convert AudioBufferList to CMSampleBuffer
Re: Convert AudioBufferList to CMSampleBuffer
- Subject: Re: Convert AudioBufferList to CMSampleBuffer
- From: Heinrich Fink <email@hidden>
- Date: Wed, 09 May 2012 08:51:10 +0200
hi patrick,
> CMSampleTimingInfo timing = { CMTimeMakeWithSeconds(1 / 44100.0, 1), kCMTimeZero, kCMTimeInvalid };
This might not be doing what you expect. CMTimeMakeWithSeconds(1 / 44100.0, 1) will actually be rounded off to [value=0, timescale=1], meaning your sample timing info will contain a duration of zero, which I am sure is not what you aimed for. Use CMTimeMake(1, 44100) instead.
Also, don’t forget to set a proper presentation time stamp for any CMSampleBuffer instances other than your first chunk of audio data.
I recommend you to look over the header documentation in CMSampleBuffer.h about CMSampleBufferCreate, especially the section "Example of usage for uncompressed non-interleaved audio:”. This really is the best source of documentation regarding CoreMedia.
best regards,
Heinrich
On May 8, 2012, at 22:40 , patrick machielse wrote:
> On iOS I need to write data coming in from an AUGraph/Unit to file. To this end I need to convert sample data contained in an AudioBufferList to a CMSampleBuffer in order to append it to a AVAssetWriterInput.
>
> It seems there isn't a lot of info available on how to do that exactly (and successfully). I've managed to come up with the following code, which uses an available ASBD struct:
>
> - (void)recordData:(AudioBufferList *)data frames:(UInt32)numberOfFrames
> {
> CMSampleBufferRef buff = NULL;
> CMFormatDescriptionRef format = NULL;
> OSStatus error = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &asbd, 0, NULL, 0, NULL, NULL, &format);
>
> CMSampleTimingInfo timing = { CMTimeMakeWithSeconds(1 / 44100.0, 1), kCMTimeZero, kCMTimeInvalid };
> error = CMSampleBufferCreate(kCFAllocatorDefault, NULL, false, NULL, NULL, format, numberOfFrames, 1, &timing, 0, NULL, &buff);
>
> error = CMSampleBufferSetDataBufferFromAudioBufferList(buff, kCFAllocatorDefault, kCFAllocatorDefault, 0, data);
> if ( error ) { NSLog(@"CMSampleBufferSetDataBufferFromAudioBufferList returned error: %ld", error); }
>
>
> In the last line the error is '-12731': kCMSampleBufferError_RequiredParameterMissing. I'm not sure which that should be, there are so many?
>
> Has anyone solved this before?
>
> Thanks,
>
> patrick
> --
> Patrick Machielse
> Hieper Software
>
> http://www.hieper.nl
> email@hidden
>
>
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