ExtAudioFileConvert questions
ExtAudioFileConvert questions
- Subject: ExtAudioFileConvert questions
- From: uɐıʇəqɐz pnoqɥɒɯ <email@hidden>
- Date: Thu, 7 Jan 2010 18:12:36 -0800
Hi everyone. I'm making some progress on taking a compressed (mp3) sound and saving it as PCM. In addition, I wanted to split the original file into chunks that are 2 seconds long, within the same process. I seem to be successful, but I am a little concerned as to why.
As I read blocks of audio and write the files out, I check to see if I am about to write a chunk that would make my file exceed my 2 second limit. If so, I write enough to get to 2 seconds, close the file, and then open a new file and write the remainder into the new file, and then read more data. Something like this:
framesInTimedSegment += numFrames;
if ((framesInTimedSegment > (2.0 * sampleRate)) && (j < 5)) {
UInt32 newNumFrames = numFrames;
numFrames = framesInTimedSegment - (2.0 * sampleRate);
newNumFrames -= numFrames;
UInt32 segmentOffset = newNumFrames * numChannels * 2; // Question A
error = ExtAudioFileWrite(segmentFile, newNumFrames, &fillBufList); // Question B
// handle this error! We might have an interruption
if (segmentFile) ExtAudioFileDispose(segmentFile);
XThrowIfError(ExtAudioFileCreateWithURL(urlArray[++j], kAudioFileCAFType, &dstFormat, NULL, kAudioFileFlags_EraseFile, &breakoutFile), "ExtAudioFileCreateWithURL failed! - segmentFile");
size = sizeof(clientFormat);
XThrowIfError(ExtAudioFileSetProperty(segmentFile, kExtAudioFileProperty_ClientDataFormat, size, &clientFormat), "couldn't set destination client format");
fillBufList.mBuffers[0].mData = srcBuffer + segmentOffset;
fillBufList.mBuffers[0].mDataByteSize = numFrames * fillBufList.mBuffers[0].mNumberChannels * 2;
framesInTimedSegment = numFrames;
}
error = ExtAudioFileWrite(segmentFile, numFrames, &fillBufList);
Here are my questions (I have tried to label the relevant line):
A: Is there a better way to find the offset into my buffer so I don't erroneously hard code some value in there? For example, is there a blessed way to get dataOffsetFromFrameNumber?
B: If ExtAudioFileWrite is doing the conversion from compressed to decompressed, then shouldn't I have to worry about playing with frame numbers and offsets when I am dealing with compressed data? Should I instead be converting the file first, either to a PCM file or into memory, and then split that PCM?
Thanks!
-mahboud _______________________________________________
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