Question

我的代码基于Learning Core Audio第6章中的代码。

此函数用于获取输入文件并将该文件中的数据包复制到输出文件。我正在使用它将许多输入文件的数据写入一个输出文件，并且它运行良好。

我遇到的唯一问题是当我添加一个新的输入文件并将startPacketPosition设置为输出文件中已经写入数据包的区域时。它用新数据替换旧数据。

有没有办法在不替换现有数据的情况下将新数据包写入文件。这就像为歌曲文件添加声音效果而不替换任何歌曲数据。

如果使用AudioFileWritePackets无法做到这一点，那么最佳选择是什么？

static void writeInputFileToOutputFile(AudioStreamBasicDescription *format, ExtAudioFileRef *inputFile, AudioFileID *outputFile, UInt32 *startPacketPosition) {
    //determine the size of the output buffer
    UInt32 outputBufferSize = 32 * 1024; //32kb
    UInt32 sizePerPacket = format->mBytesPerPacket;
    UInt32 packetsPerBuffer = outputBufferSize / sizePerPacket;

    //allocate a buffer for recieving the data
    UInt8 *outputBuffer = (UInt8 *)malloc(sizeof(UInt8) * outputBufferSize);

    //read-convert-write
    while (1) {
        AudioBufferList convertedData; //create an audio buffer list
        convertedData.mNumberBuffers = 1; //with only one buffer
        //set the properties on the single buffer
        convertedData.mBuffers[0].mNumberChannels = format->mChannelsPerFrame;
        convertedData.mBuffers[0].mDataByteSize = outputBufferSize;
        convertedData.mBuffers[0].mData = outputBuffer;

        //get the number of frames and buffer data from the input file
        UInt32 framesPerBuffer = packetsPerBuffer;
        CheckError(ExtAudioFileRead(*inputFile, &framesPerBuffer, &convertedData), "ExtAudioFileRead");

        //if framecount is 0, were finished
        if (framesPerBuffer == 0) {
            return;
        }

        UInt32 bytes = format->mBytesPerPacket;
        CheckError(AudioFileWritePackets(*outputFile, false, framesPerBuffer*bytes, NULL, *startPacketPosition, &framesPerBuffer, convertedData.mBuffers[0].mData), "AudioFileWritePackets");

        //increase the ouput file packet position
        *startPacketPosition += framesPerBuffer;
    }
    free(outputBuffer);

}

Answer 1

我找到了一种使用AVMutableComposition实现此目的的方法

-(void)addInputAsset:(AVURLAsset *)input toOutputComposition:(AVMutableComposition *)composition atTime:(float)seconds {
    //add the input to the composition
    AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVAssetTrack *clipAudioTrack = [[input tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    //set the start time
    int sampleRate = 44100;
    CMTime nextClipStartTime = CMTimeMakeWithSeconds(seconds, sampleRate);
    [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, input.duration) ofTrack:clipAudioTrack atTime:nextClipStartTime error:nil];
}

要使用此方法混合两个音频文件，您可以这样称呼它：

-(void)mixAudio {
    //create a mutable compsition
    AVMutableComposition* composition = [AVMutableComposition composition];

    //audio file 1
    NSURL *url1 = [NSURL URLWithString:@"path/to/file1.mp3"];
    AVURLAsset* asset1 = [[AVURLAsset alloc]initWithURL:url1 options:nil];
    [self addInputAsset:asset1 toOutputComposition:composition atTime:0.0];

    //audio file 2
    NSURL *url2 = [NSURL URLWithString:@"path/to/file2.aif"];
    AVURLAsset* asset2 = [[AVURLAsset alloc]initWithURL:url2 options:nil];
    [self addInputAsset:asset2 toOutputComposition:composition atTime:0.2];

    //create the export session
    AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:AVAssetExportPresetAppleM4A];
    if (exportSession == nil) {
        //ERROR: abort
    }

    // configure export session  output with all our parameters
    exportSession.outputURL = [NSURL fileURLWithPath:@"path/to/output_file.m4a"]; // output path
    exportSession.outputFileType = AVFileTypeAppleM4A; // output file type

    //export the file
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        if (AVAssetExportSessionStatusCompleted == exportSession.status) {
            NSLog(@"AVAssetExportSessionStatusCompleted");
        } else if (AVAssetExportSessionStatusFailed == exportSession.status) {
            NSLog(@"AVAssetExportSessionStatusFailed");
        } else {
            NSLog(@"Export Session Status: %ld", (long)exportSession.status);
        }
    }];
}

是否可以使用AudioFileWritePackets写入文件而不替换该文件上的现有数据？

1 个答案: