我正在将AVMutableAudioMix应用于我创建的资产，资产通常包含3-5个音轨（无视频）。目标是在整个播放时间内添加几个音量命令，即我想将音量设置为1秒，0.5秒，2秒，然后是0.1或3秒时的任何值。我刚刚尝试使用AVPlayer执行此操作，但稍后在将AVSession导出到文件时也会使用它。问题是它似乎只关心第一个volume命令，似乎忽略了所有后来的volume命令。如果第一个命令是将音量设置为0.1，那么该音轨的剩余部分将成为该音轨的永久音量。尽管看起来你应该能够添加任意数量的这些命令，但看到AVMutableAudioMix的“inputParameters”成员实际上是一个NSArray，它是AVMutableAudioMixInputParameter的系列。有人想出来了吗？
编辑：我认为这部分原因。我可以在某个轨道上添加几个音量变化。但时间似乎有点偏离，我不知道如何解决这个问题。例如，在5秒时将音量设置为0.0，然后在10秒时设置为1.0，然后在15秒时将音量设置为0.0将使您假设音量将在这些时间点立即开启和关闭，但结果总是非常不可预测，随着渐变声音发生，有时工作（突然的音量变化与setVolume预期的一样）。如果有人让AudioMix工作，请提供一个例子。
答案 0 :(得分：8)
我用来改变音轨音量的代码是：
AVURLAsset *soundTrackAsset = [[AVURLAsset alloc]initWithURL:trackUrl options:nil];
AVMutableAudioMixInputParameters *audioInputParams = [AVMutableAudioMixInputParameters audioMixInputParameters];
[audioInputParams setVolume:0.5 atTime:kCMTimeZero];
[audioInputParams setTrackID:[[[soundTrackAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] trackID]];
audioMix = [AVMutableAudioMix audioMix];
audioMix.inputParameters = [NSArray arrayWithObject:audioInputParams];
不要忘记将audiomix添加到AVAssetExportSession
exportSession.audioMix = audioMix;
但是，我注意到它不适用于所有格式，因此如果您一直遇到AVFoundation问题，可以使用此功能更改存储文件的音量级别。但是，这个功能可能很慢。
-(void) ScaleAudioFileAmplitude:(NSURL *)theURL: (float) ampScale {
OSStatus err = noErr;
ExtAudioFileRef audiofile;
ExtAudioFileOpenURL((CFURLRef)theURL, &audiofile);
assert(audiofile);
// get some info about the file's format.
AudioStreamBasicDescription fileFormat;
UInt32 size = sizeof(fileFormat);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_FileDataFormat, &size, &fileFormat);
// we'll need to know what type of file it is later when we write
AudioFileID aFile;
size = sizeof(aFile);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_AudioFile, &size, &aFile);
AudioFileTypeID fileType;
size = sizeof(fileType);
err = AudioFileGetProperty(aFile, kAudioFilePropertyFileFormat, &size, &fileType);
// tell the ExtAudioFile API what format we want samples back in
AudioStreamBasicDescription clientFormat;
bzero(&clientFormat, sizeof(clientFormat));
clientFormat.mChannelsPerFrame = fileFormat.mChannelsPerFrame;
clientFormat.mBytesPerFrame = 4;
clientFormat.mBytesPerPacket = clientFormat.mBytesPerFrame;
clientFormat.mFramesPerPacket = 1;
clientFormat.mBitsPerChannel = 32;
clientFormat.mFormatID = kAudioFormatLinearPCM;
clientFormat.mSampleRate = fileFormat.mSampleRate;
clientFormat.mFormatFlags = kLinearPCMFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved;
err = ExtAudioFileSetProperty(audiofile, kExtAudioFileProperty_ClientDataFormat, sizeof(clientFormat), &clientFormat);
// find out how many frames we need to read
SInt64 numFrames = 0;
size = sizeof(numFrames);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_FileLengthFrames, &size, &numFrames);
// create the buffers for reading in data
AudioBufferList *bufferList = malloc(sizeof(AudioBufferList) + sizeof(AudioBuffer) * (clientFormat.mChannelsPerFrame - 1));
bufferList->mNumberBuffers = clientFormat.mChannelsPerFrame;
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
bufferList->mBuffers[ii].mDataByteSize = sizeof(float) * numFrames;
bufferList->mBuffers[ii].mNumberChannels = 1;
bufferList->mBuffers[ii].mData = malloc(bufferList->mBuffers[ii].mDataByteSize);
}
// read in the data
UInt32 rFrames = (UInt32)numFrames;
err = ExtAudioFileRead(audiofile, &rFrames, bufferList);
// close the file
err = ExtAudioFileDispose(audiofile);
// process the audio
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
float *fBuf = (float *)bufferList->mBuffers[ii].mData;
for (int jj=0; jj < rFrames; ++jj) {
*fBuf = *fBuf * ampScale;
fBuf++;
}
}
// open the file for writing
err = ExtAudioFileCreateWithURL((CFURLRef)theURL, fileType, &fileFormat, NULL, kAudioFileFlags_EraseFile, &audiofile);
// tell the ExtAudioFile API what format we'll be sending samples in
err = ExtAudioFileSetProperty(audiofile, kExtAudioFileProperty_ClientDataFormat, sizeof(clientFormat), &clientFormat);
// write the data
err = ExtAudioFileWrite(audiofile, rFrames, bufferList);
// close the file
ExtAudioFileDispose(audiofile);
// destroy the buffers
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
free(bufferList->mBuffers[ii].mData);
}
free(bufferList);
bufferList = NULL;
}
另请注意，您可能需要根据音量值的来源微调所需的ampScale。系统卷从0到1，可以通过调用AudioSessionGetProperty
获得Float32 volume;
UInt32 dataSize = sizeof(Float32);
AudioSessionGetProperty (
kAudioSessionProperty_CurrentHardwareOutputVolume,
&dataSize,
&volume
);
答案 1 :(得分：2)
由于API更改，音频扩展工具箱功能不再起作用。现在需要您设置类别。设置导出属性时，我收到错误代码'？cat'（NSError将以十进制格式打印出来）。
以下是iOS 5.1中现在可用的代码。它也非常缓慢，只是看起来我会说慢几倍。它也是内存密集型的，因为它似乎将文件加载到内存中，这会为10MB的mp3文件生成内存警告。
-(void) scaleAudioFileAmplitude:(NSURL *)theURL withAmpScale:(float) ampScale
{
OSStatus err = noErr;
ExtAudioFileRef audiofile;
ExtAudioFileOpenURL((CFURLRef)theURL, &audiofile);
assert(audiofile);
// get some info about the file's format.
AudioStreamBasicDescription fileFormat;
UInt32 size = sizeof(fileFormat);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_FileDataFormat, &size, &fileFormat);
// we'll need to know what type of file it is later when we write
AudioFileID aFile;
size = sizeof(aFile);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_AudioFile, &size, &aFile);
AudioFileTypeID fileType;
size = sizeof(fileType);
err = AudioFileGetProperty(aFile, kAudioFilePropertyFileFormat, &size, &fileType);
// tell the ExtAudioFile API what format we want samples back in
AudioStreamBasicDescription clientFormat;
bzero(&clientFormat, sizeof(clientFormat));
clientFormat.mChannelsPerFrame = fileFormat.mChannelsPerFrame;
clientFormat.mBytesPerFrame = 4;
clientFormat.mBytesPerPacket = clientFormat.mBytesPerFrame;
clientFormat.mFramesPerPacket = 1;
clientFormat.mBitsPerChannel = 32;
clientFormat.mFormatID = kAudioFormatLinearPCM;
clientFormat.mSampleRate = fileFormat.mSampleRate;
clientFormat.mFormatFlags = kLinearPCMFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved;
err = ExtAudioFileSetProperty(audiofile, kExtAudioFileProperty_ClientDataFormat, sizeof(clientFormat), &clientFormat);
// find out how many frames we need to read
SInt64 numFrames = 0;
size = sizeof(numFrames);
err = ExtAudioFileGetProperty(audiofile, kExtAudioFileProperty_FileLengthFrames, &size, &numFrames);
// create the buffers for reading in data
AudioBufferList *bufferList = malloc(sizeof(AudioBufferList) + sizeof(AudioBuffer) * (clientFormat.mChannelsPerFrame - 1));
bufferList->mNumberBuffers = clientFormat.mChannelsPerFrame;
//printf("bufferList->mNumberBuffers = %lu \n\n", bufferList->mNumberBuffers);
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
bufferList->mBuffers[ii].mDataByteSize = sizeof(float) * numFrames;
bufferList->mBuffers[ii].mNumberChannels = 1;
bufferList->mBuffers[ii].mData = malloc(bufferList->mBuffers[ii].mDataByteSize);
}
// read in the data
UInt32 rFrames = (UInt32)numFrames;
err = ExtAudioFileRead(audiofile, &rFrames, bufferList);
// close the file
err = ExtAudioFileDispose(audiofile);
// process the audio
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
float *fBuf = (float *)bufferList->mBuffers[ii].mData;
for (int jj=0; jj < rFrames; ++jj) {
*fBuf = *fBuf * ampScale;
fBuf++;
}
}
// open the file for writing
err = ExtAudioFileCreateWithURL((CFURLRef)theURL, fileType, &fileFormat, NULL, kAudioFileFlags_EraseFile, &audiofile);
NSError *error = NULL;
/*************************** You Need This Now ****************************/
AVAudioSession *session = [AVAudioSession sharedInstance];
[session setCategory:AVAudioSessionCategoryAudioProcessing error:&error];
/************************* End You Need This Now **************************/
// tell the ExtAudioFile API what format we'll be sending samples in
err = ExtAudioFileSetProperty(audiofile, kExtAudioFileProperty_ClientDataFormat, sizeof(clientFormat), &clientFormat);
error = [NSError errorWithDomain:NSOSStatusErrorDomain
code:err
userInfo:nil];
NSLog(@"Error: %@", [error description]);
// write the data
err = ExtAudioFileWrite(audiofile, rFrames, bufferList);
// close the file
ExtAudioFileDispose(audiofile);
// destroy the buffers
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii) {
free(bufferList->mBuffers[ii].mData);
}
free(bufferList);
bufferList = NULL;
}
答案 2 :(得分：0)
感谢您在此帖中提供的帮助。 我只想补充一点，因为你应该将AVAudioSession恢复到原来状态，否则你最终不会玩任何东西。
AVAudioSession *session = [AVAudioSession sharedInstance];
NSString *originalSessionCategory = [session category];
[session setCategory:AVAudioSessionCategoryAudioProcessing error:&error];
...
...
// restore category
[session setCategory:originalSessionCategory error:&error];
if(error)
NSLog(@"%@",[error localizedDescription]);
干杯
答案 3 :(得分：0)
如需设置不同音量的可变轨道，您可以在代码
下使用self.audioMix = [AVMutableAudioMix audioMix];
AVMutableAudioMixInputParameters *audioInputParams = [AVMutableAudioMixInputParameters audioMixInputParameters];
[audioInputParams setVolume:0.1 atTime:kCMTimeZero];
[audioInputParams setVolume:0.1 atTime:kCMTimeZero];
audioInputParams.trackID = compositionAudioTrack2.trackID;
AVMutableAudioMixInputParameters *audioInputParams1 = [AVMutableAudioMixInputParameters audioMixInputParameters];
[audioInputParams1 setVolume:0.9 atTime:kCMTimeZero];
audioInputParams1.trackID = compositionAudioTrack1.trackID;
AVMutableAudioMixInputParameters *audioInputParams2 = [AVMutableAudioMixInputParameters audioMixInputParameters];
[audioInputParams2 setVolume:0.3 atTime:kCMTimeZero];
audioInputParams2.trackID = compositionAudioTrack.trackID;
self.audioMix.inputParameters =[NSArray arrayWithObjects:audioInputParams,audioInputParams1,audioInputParams2, nil];