使用AVMutableAudioMix调整卷资产范围内的曲目 [英] Using AVMutableAudioMix to adjust volumes for tracks within asset

问题描述

我申请一个AVMutableAudioMix到我创建了一个资产，资产一般由3-5音轨（无视频）。我们的目标是在整个播放时间增加几个数量的命令，即我想在2秒将音量设置为0.1以1秒0.5，那么0.1或任何在3秒。我只是现在正试图与AVPlayer这样做，但在出口到AVSession文件时也会用到它。现在的问题是，它似乎只关心先容的命令，似乎忽略后面的所有卷的命令。如果第一个命令是将音量设置为0.1，这将是这条赛道对于该资产的其他永久音量。尽管它真的看起来像你应该可以添加任意数量的这些命令，看到AVMutableAudioMix的inputParameters成员确实是一个NSArray这是该系列AVMutableAudioMixInputParameter年代。任何人都想通了这一点？

I'm applying an AVMutableAudioMix to a asset I've created, the asset generally consists of 3-5 audio tracks (no video). The goal is to add several volume commands throughout the play time, ie I'd like to set the volume to 0.1 at 1 seconds, 0.5 at 2 seconds, then 0.1 or whatever at 3 seconds. I'm just now trying to do this with an AVPlayer but will also later use it when exporting the AVSession to a file. The problem is that it only seems to care about the first volume command, and seem to ignore all later volume commands. If the first command is to set the volume to 0.1, that will be the permanent volume for this track for the rest of this asset. Despite it really looks like you should be able to add any number of these commands, seeing as the "inputParameters" member of AVMutableAudioMix is really an NSArray which is the series of AVMutableAudioMixInputParameter's. Anyone figured this out?

编辑：我想通了这部分的。我能够在整个某一轨道添加若干量的变化。但计时出现的路要走，我不知道如何解决这个问题。例如设定在5秒钟，然后1.0在10秒钟，然后回到在15秒时0.0的容积为0.0会令你承担的音量会去和关闭及时在这些时序，但结果总是很未经predictable，随着声音的斜坡回事，有时工作（与从setVolume预期突然的音量变化）。如果有人得到了AudioMix工作，请提供一个例子。

I figured this partly out. I'm able to add several volume changes throughout a certain track. But the timings appear way off, I'm not sure how to fix that. For example setting the volume to 0.0 at 5 seconds, then 1.0 at 10 seconds and then back to 0.0 at 15 seconds would make you assume the volume would go on and off promptly at those timings, but the results are always very unpredictable, with ramping of sounds going on, and sometimes working (with sudden volume changes as expected from setVolume). If anyone got the AudioMix to work, please provide an example.

推荐答案

在code我用它来改变轨道体积为：

The code I use to change the track volume is:

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];

不要忘了给audiomix添加到您的AVAssetExportSession

Don't forget to add the audiomix to your AVAssetExportSession

exportSession.audioMix = audioMix;

不过，我发现它并不适用于所有格式工作，所以如果你一直有问题与AVF​​oundation您可以使用此功能来改变存储文件的音量。然而，这个功能可能是相当缓慢的。

However, I notice it does not work with all formats so You can use this function to change the volume level of an stored file if you keep having issues with AVFoundation. However, this function could be quite slow.

-(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;

 }

另外请注意，你可能需要将ampScale您根据您的音量值是来自要微调。系统体积从0到1，并且可以通过调用AudioSessionGetProperty获得

Please also note that you may need to fine tune the ampScale you want depending where your volume value is coming from. The system volume goes from 0 to 1 and can be obtained by calling AudioSessionGetProperty

Float32 volume;
UInt32 dataSize = sizeof(Float32);
AudioSessionGetProperty (
                         kAudioSessionProperty_CurrentHardwareOutputVolume,
                         &dataSize,
                         &volume
                        );

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