Re: trouble creating working Apple Lossless file under iOS 3.2
Re: trouble creating working Apple Lossless file under iOS 3.2
- Subject: Re: trouble creating working Apple Lossless file under iOS 3.2
- From: Ian Esten <email@hidden>
- Date: Fri, 05 Nov 2010 00:59:48 -0700
ALAC data can be written to either CAF or Apple MPEG-4 audio formats. Perhaps if you switch to MPEG-4 you will get files that Quicktime and iTunes can play. I experienced the same problem with AAC data - Quicktime and iTunes would not play the files I created, but AFConvert could convert them back to PCM no problem.
Ian
On Nov 4, 2010, at 11:09 PM, Christopher Penrose wrote:
> 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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