使用AVMutableAudioMix调整资产中轨道的音量

Question

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0.1秒1秒,0.5秒2秒,然后0.1或3秒钟的任何值.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:我想到了这一点.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,请提供一个示例.

Answer 1

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
                        );