Hi all -
I'm having no luck converting a VBR MP3 network stream into an uncompresed
format file. Been banging my head on it for a few days.
The mp3 stream could be either 1 or 2 channels. Currently I'm having
trouble getting just 1 channel to work.
I think where I'm going wrong is in determining the number of frames to
send to ExtAudioFileWrite.
I'm trying to write to the file inside the Audio File Stream service
callback:
static void SR_MyAFSPacketsProc ( void *inClientData,
UInt32 inNumberBytes, UInt32 inNumberPackets,
const void *inInputData, AudioStreamPacketDescription
*inPacketDescriptions ) {
}
Because the input file stream is a VBR MP3,
inPacketDescriptions[0].mVariableFramesInPacket is always 0. And the
mp3StreamASBD's mFramesPerPacket makes no sense. Also *mBytesPerFrame is 0
(I understand this is to be expected for the compressed mp3 format) *
For my stream's ASBD mFramesPerPacket is 576 and a callback to the
AudioFileStream service packet callback may offer 12235 bytes in 233
packets. If I use the stream's mFramesPerPacket of 576 * 233 packets, I
get 134208 frames. 134208 frames for 12235 bytes seems a bit off.
Anyone out there have a suggestion how to determine the number of frames to
pass to ExtAudioFileWrite?
I think I'm doing everything else correctly:
This is the ASBD I am using for the output file:
dstFormat.mSampleRate = sampleRate;
dstFormat.mChannelsPerFrame = channelCount;
dstFormat.mFormatID = kAudioFormatLinearPCM;
dstFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger |
kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsPacked;
dstFormat.mBitsPerChannel = 16;
dstFormat.mBytesPerPacket = dstFormat.mBytesPerFrame = 2 *
dstFormat.mChannelsPerFrame;
dstFormat.mFramesPerPacket = 1;
In the AudioFileStream Property listener callback for
kAudioFileStreamProperty_ReadyToProducePackets, I use the output file ASBD
to both create the file (ExtAudioFileCreateWithURL) and to set the
clientDataFormat on that file (ExtAudioFileSetProperty with
kExtAudioFileProperty_ClientDataFormat).
NSURL *url = [NSURL fileURLWithPath:@"/testout/lpcmout.caf"];
CFURLRef sourceURL = (__bridge CFURLRef) url;
SR_CheckError(ExtAudioFileCreateWithURL(sourceURL, kAudioFileCAFType,
&sr_fileDesc, *NULL*, kAudioFileFlags_EraseFile, &sr_audioFile), "create
output file failed");
SR_CheckError(ExtAudioFileSetProperty(sr_audioFile,
kExtAudioFileProperty_ClientDataFormat,
sizeof (AudioStreamBasicDescription), &sr_fileDesc), "Couldn't set client
data format on input ext file");
Thank you-
Matt
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list ([email protected])
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/coreaudio-api/archive%40mail-archive.com
This email sent to [email protected]
