我试图反转fruit = 'orange';
namesWorkspace = who;
vars = namesWorkspace(~cellfun('isempty',regexpi(namesWorkspace, fruit)));
try
assignin('base',fruit,evalin('base',vars{1}))
catch
error('No matching variable name!')
end
音频并将其保存到文件中。为了清楚起见，我已经使用问题https://github.com/ksenia-lyagusha/AudioReverse.git
应用程序从bundle中获取AVAsset视频文件，将其作为单个mp4文件导出到沙箱中的Temporary文件夹，然后尝试从那里读取它，反向并保存结果文件。
临时m4a文件正常。
我的反向部分的唯一结果是m4a中带有白噪声的音频文件。
下面是代码的一部分，负责撤销Sandbox。它基于相关问题
但是，它对我没用。
AVAsset如果我将OSStatus theErr = noErr;
UInt64 fileDataSize = 0;
AudioFileID inputAudioFile;
AudioStreamBasicDescription theFileFormat;
UInt32 thePropertySize = sizeof(theFileFormat);
theErr = AudioFileOpenURL((__bridge CFURLRef)[NSURL URLWithString:inputPath], kAudioFileReadPermission, 0, &inputAudioFile);
thePropertySize = sizeof(fileDataSize);
theErr = AudioFileGetProperty(inputAudioFile, kAudioFilePropertyAudioDataByteCount, &thePropertySize, &fileDataSize);
UInt32 ps = sizeof(AudioStreamBasicDescription) ;
AudioFileGetProperty(inputAudioFile, kAudioFilePropertyDataFormat, &ps, &theFileFormat);
UInt64 dataSize = fileDataSize;
void *theData = malloc(dataSize);
// set up output file
AudioFileID outputAudioFile;
AudioStreamBasicDescription myPCMFormat;
myPCMFormat.mSampleRate = 44100;
myPCMFormat.mFormatID = kAudioFormatLinearPCM;
// kAudioFormatFlagsCanonical is deprecated
myPCMFormat.mFormatFlags = kAudioFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved;
myPCMFormat.mChannelsPerFrame = 1;
myPCMFormat.mFramesPerPacket = 1;
myPCMFormat.mBitsPerChannel = 32;
myPCMFormat.mBytesPerPacket = (myPCMFormat.mBitsPerChannel / 8) * myPCMFormat.mChannelsPerFrame;
myPCMFormat.mBytesPerFrame = myPCMFormat.mBytesPerPacket;
NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"ReverseAudio.caf"];
NSURL *outputURL = [NSURL fileURLWithPath:exportPath];
theErr = AudioFileCreateWithURL((__bridge CFURLRef)outputURL,
kAudioFileCAFType,
&myPCMFormat,
kAudioFileFlags_EraseFile,
&outputAudioFile);
//Read data into buffer
//if readPoint = dataSize, then bytesToRead = 0 in while loop and
//it is endless
SInt64 readPoint = dataSize-1;
UInt64 writePoint = 0;
while(readPoint > 0)
{
UInt32 bytesToRead = 2;
AudioFileReadBytes(inputAudioFile, false, readPoint, &bytesToRead, theData);
// bytesToRead is now the amount of data actually read
UInt32 bytesToWrite = bytesToRead;
AudioFileWriteBytes(outputAudioFile, false, writePoint, &bytesToWrite, theData);
// bytesToWrite is now the amount of data actually written
writePoint += bytesToWrite;
readPoint -= bytesToRead;
}
free(theData);
AudioFileClose(inputAudioFile);
AudioFileClose(outputAudioFile);
中的文件类型从AudioFileCreateWithURL更改为另一个，则根本不会在kAudioFileCAFType中创建结果文件。
感谢您的帮助。
答案 0 :(得分：4)
由于您的输入和输出文件格式不兼容，您会收到白噪声。您有不同的采样率和频道，可能还有其他差异。要完成这项工作，您需要在读取和写入之间使用通用（PCM）格式。对于新的（ish）AVAudio框架来说，这是一个合理的工作。我们从文件读取到PCM，随机播放缓冲区，然后从PCM写入文件。这种方法没有针对大型文件进行优化，因为所有数据都可以一次性读入缓冲区，但足以让您入门。
您可以从getAudioFromVideo完成版块调用此方法。为清楚起见，忽略了错误处理。
- (void)readAudioFromURL:(NSURL*)inURL reverseToURL:(NSURL*)outURL {
//prepare the in and outfiles
AVAudioFile* inFile =
[[AVAudioFile alloc] initForReading:inURL error:nil];
AVAudioFormat* format = inFile.processingFormat;
AVAudioFrameCount frameCount =(UInt32)inFile.length;
NSDictionary* outSettings = @{
AVNumberOfChannelsKey:@(format.channelCount)
,AVSampleRateKey:@(format.sampleRate)};
AVAudioFile* outFile =
[[AVAudioFile alloc] initForWriting:outURL
settings:outSettings
error:nil];
//prepare the forward and reverse buffers
self.forwaredBuffer =
[[AVAudioPCMBuffer alloc] initWithPCMFormat:format
frameCapacity:frameCount];
self.reverseBuffer =
[[AVAudioPCMBuffer alloc] initWithPCMFormat:format
frameCapacity:frameCount];
//read file into forwardBuffer
[inFile readIntoBuffer:self.forwaredBuffer error:&error];
//set frameLength of reverseBuffer to forwardBuffer framelength
AVAudioFrameCount frameLength = self.forwaredBuffer.frameLength;
self.reverseBuffer.frameLength = frameLength;
//iterate over channels
//stride is 1 or 2 depending on interleave format
NSInteger stride = self.forwaredBuffer.stride;
for (AVAudioChannelCount channelIdx = 0;
channelIdx < self.forwaredBuffer.format.channelCount;
channelIdx++) {
float* forwaredChannelData =
self.forwaredBuffer.floatChannelData[channelIdx];
float* reverseChannelData =
self.reverseBuffer.floatChannelData[channelIdx];
int32_t reverseIdx = 0;
//iterate over samples, allocate to reverseBuffer in reverse order
for (AVAudioFrameCount frameIdx = frameLength;
frameIdx >0;
frameIdx--) {
float sample = forwaredChannelData[frameIdx*stride];
reverseChannelData[reverseIdx*stride] = sample;
reverseIdx++;
}
}
//write reverseBuffer to outFile
[outFile writeFromBuffer:self.reverseBuffer error:nil];
}
答案 1 :(得分：0)
我无法在您的代码中找到问题，但我建议您使用AVAsset撤消AVAssetWriter。以下代码基于iOS reverse audio through AVAssetWritet。我在那里添加了其他方法以使其工作。最后我得到了反转文件。
static NSMutableArray *samples;
static OSStatus sampler(CMSampleBufferRef sampleBuffer, CMItemCount index, void *refcon)
{
[samples addObject:(__bridge id _Nonnull)(sampleBuffer)];
return noErr;
}
- (void)reversePlayAudio:(NSURL *)inputURL
{
AVAsset *asset = [AVAsset assetWithURL:inputURL];
AVAssetReader* reader = [[AVAssetReader alloc] initWithAsset:asset error:nil];
AVAssetTrack* audioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
NSMutableDictionary* audioReadSettings = [NSMutableDictionary dictionary];
[audioReadSettings setValue:[NSNumber numberWithInt:kAudioFormatLinearPCM]
forKey:AVFormatIDKey];
AVAssetReaderTrackOutput* readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:audioReadSettings];
[reader addOutput:readerOutput];
[reader startReading];
NSDictionary *outputSettings = @{AVFormatIDKey : @(kAudioFormatMPEG4AAC),
AVSampleRateKey : @(44100.0),
AVNumberOfChannelsKey : @(1),
AVEncoderBitRateKey : @(128000),
AVChannelLayoutKey : [NSData data]};
AVAssetWriterInput *writerInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeAudio
outputSettings:outputSettings];
NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"reverseAudio.m4a"];
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];
NSError *writerError = nil;
AVAssetWriter *writer = [[AVAssetWriter alloc] initWithURL:exportURL
fileType:AVFileTypeAppleM4A
error:&writerError];
[writerInput setExpectsMediaDataInRealTime:NO];
writer.shouldOptimizeForNetworkUse = NO;
[writer addInput:writerInput];
[writer startWriting];
[writer startSessionAtSourceTime:kCMTimeZero];
CMSampleBufferRef sample;// = [readerOutput copyNextSampleBuffer];
samples = [[NSMutableArray alloc] init];
while (sample != NULL) {
sample = [readerOutput copyNextSampleBuffer];
if (sample == NULL)
continue;
CMSampleBufferCallForEachSample(sample, &sampler, NULL);
CFRelease(sample);
}
NSArray* reversedSamples = [[samples reverseObjectEnumerator] allObjects];
for (id reversedSample in reversedSamples) {
if (writerInput.readyForMoreMediaData) {
[writerInput appendSampleBuffer:(__bridge CMSampleBufferRef)(reversedSample)];
}
else {
[NSThread sleepForTimeInterval:0.05];
}
}
[samples removeAllObjects];
[writerInput markAsFinished];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(queue, ^{
[writer finishWritingWithCompletionHandler:^{
// writing is finished
// reversed audio file in TemporaryDirectory in the Sandbox
}];
});
}
代码的已知问题。