trouble creating working Apple Lossless file under iOS 3.2
trouble creating working Apple Lossless file under iOS 3.2
- Subject: trouble creating working Apple Lossless file under iOS 3.2
- From: Christopher Penrose <email@hidden>
- Date: Thu, 4 Nov 2010 23:09:02 -0700
I am able to create Apple Lossless files with my iPad app under iOS 3.2 using either an m4a or caf transport. I receive no errors from the API. The problem is that they are unplayable -- they lock Finder, Quicktime Player, iTunes, and afplay for about 10 seconds. Upon inspection with afinfo they look normal to me (I haven't found an indication that a channel layout is needed for ALAC files to be playable). I am passing audio buffers to ExtAudioFileWrite ()which are in iOS canonical format (which might be the issue perhaps, but AIFF and WAV work fine using them).
% afinfo hobo.caf
File: hobo.caf
File type ID: caff
Data format: 2 ch, 44100 Hz, 'alac' (0x00000003) from 24-bit source, 4096 frames/packet
no channel layout.
estimated duration: 12.423 sec
audio bytes: 1784876
audio packets: 134
audio 547840 valid frames + 0 priming + 1024 remainder = 548864
bit rate: 1147286 bits per second
packet size upper bound: 15781
audio data file offset: 12288
optimized
----
% afplay hobo.caf
Error: start audio output unit (-536870185)
% ls -alt hobo.caf
-rw-r--r-- 1 penrose admin 1797164 Nov 4 22:40 hobo.caf
I use the following code fragment to configure the ASBD for Apple Lossless:
// clear output audio format ASBD
bzero(&performOutputFormat, sizeof(AudioStreamBasicDescription));
// adjust format id for Apple Lossless codec
performOutputFormat.mFormatID = kAudioFormatAppleLossless;
performOutputFormat.mSampleRate = performClientFormat.mSampleRate;
performOutputFormat.mChannelsPerFrame = performClientFormat.mChannelsPerFrame;
// adjust format flags for Apple Lossless codec
performOutputFormat.mFormatFlags = kAppleLosslessFormatFlag_24BitSourceData;
// trust the AudioFormat API to hopefully fill out the rest.
UInt32 size = sizeof(performOutputFormat);
OSStatus err = AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &size, &performOutputFormat);
// whine about failure should it occur
if (err != noErr) {
[STButler alertPanelTitle:@"Audio Export Error" message:
@"Failure to get format requirements for Apple Lossless codec."];
}
I open the file for writing with:
err = ExtAudioFileCreateWithURL (cfFileUrl, fileType, &performOutputFormat, NULL, kAudioFileFlags_EraseFile, &recordPerformAudioFileRef);
I write buffers to the the audiofileref once it is opened using:
OSStatus err = ExtAudioFileWrite(recordPerformAudioFileRef, bufferCount, currentAudioBuffer);
I have used the same code base to write playable AIFF and WAV files without issue. I am not sure what I have neglected here. Thanks for any input.
Christopher
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| References: | |
| | >afinfo (From: email@hidden <email@hidden>) |
| | >Re: afinfo (From: Jean-Daniel Dupas <email@hidden>) |
| | >Re: afinfo (From: Robert Martin <email@hidden>) |