如何找到正确的缓冲区大小以使用 Concentus 解压缩 Opus 文件

Question

我正在尝试编写一个 Android 应用程序（使用 Xamarin），我可以在其中录制然后播放 .opus 文件。我以前从未使用过Opus，所以请多多包涵...

我正在使用 Concentus NuGet 包 compress/decompress 音频。 Concentus 的示例代码建议使用以下内容进行记录：

// Initialize
OpusEncoder encoder = OpusEncoder.Create(48000, 1, OpusApplication.OPUS_APPLICATION_AUDIO);
encoder.Bitrate = 12000;

// Encoding loop
short[] inputAudioSamples
byte[] outputBuffer[1000];
int frameSize = 960;

int thisPacketSize = encoder.Encode(inputAudioSamples, 0, frameSize, outputBuffer, 0, outputBuffer.Length); // this throws OpusException on a failure, rather than returning a negative number

使用这些信息，我创建了以下记录方法：

    private void RecordAudio(string filename)
    {
        _outputStream = File.Open(filename, FileMode.OpenOrCreate);
        _binaryWriter = new BinaryWriter(_outputStream);
        OpusEncoder encoder = OpusEncoder.Create(AudioFormat.SampleRate, 1, OpusApplication.OPUS_APPLICATION_AUDIO);
        encoder.Bitrate = 12000;

        int frameSize = AudioFormat.SampleRate * 20 / 1000;
        short[] audioBuffer = new short[frameSize];
        byte[] outputBuffer = new byte[1000];

        _audioRecorder = new AudioRecord(
          // Hardware source of recording.
          AudioSource.Mic,
          // Frequency
          AudioFormat.SampleRate,
          // Mono or stereo
          AudioFormat.ChannelIn,
          // Audio encoding
          AudioFormat.Encoding,
          // Length of the audio clip.
          audioBuffer.Length
        );
        _audioRecorder.StartRecording();

        _isRecording = true;
        while (_isRecording)
        {
            try
            {
                // Keep reading the buffer while there is audio input.
                _audioRecorder.Read(audioBuffer, 0, audioBuffer.Length);

                int thisPacketSize = encoder.Encode(audioBuffer, 0, frameSize, outputBuffer, 0, outputBuffer.Length); // this throws OpusException on a failure, rather than returning a negative number
                Debug.WriteLine("Packet size = " + thisPacketSize);
                // Write to the audio file.
                _binaryWriter.Write(outputBuffer, 0, thisPacketSize);
            }
            catch (System.Exception ex)
            {
                Console.Out.WriteLine(ex.Message);
            }
        }
    }

查看thisPacketSize，我可以看出它是可变的。

Concentus 建议使用以下解码代码：

OpusDecoder decoder = OpusDecoder.Create(48000, 1);

// Decoding loop
byte[] compressedPacket;
int frameSize = 960; // must be same as framesize used in input, you can use OpusPacketInfo.GetNumSamples() to determine this dynamically
short[] outputBuffer = new short[frameSize];

int thisFrameSize = _decoder.Decode(compressedPacket, 0, compressedPacket.Length, outputBuffer, 0, frameSize, false);

我最初的播放想法如下：

    void PlayAudioTrack(string filename)
    {
        _inputStream = File.OpenRead(filename);
        _inputStream.Position = _recording.CurrentPosition - _recording.CurrentPosition % AudioFormat.BytesPerSample;
        OpusDecoder decoder = OpusDecoder.Create(AudioFormat.SampleRate, 1);

        int frameSize = AudioFormat.SampleRate * 20 / 1000;

        _audioTrack = new AudioTrack(
          // Stream type
          Android.Media.Stream.Music,
          // Frequency
          AudioFormat.SampleRate,
          // Mono or stereo
          AudioFormat.ChannelOut,
          // Audio encoding
          AudioFormat.Encoding,
          // Length of the audio clip.
          frameSize,
          // Mode. Stream or static.
          AudioTrackMode.Stream);

        _audioTrack.SetPositionNotificationPeriod(AudioFormat.SampleRate / 30);
        _audioTrack.PeriodicNotification += _audioTrack_PeriodicNotification;
        _audioTrack.Play();

        short[] audioBuffer = new short[frameSize];

        int bytesRead = 0;
        do
        {
            try
            {
                byte[] compressedPacket = new byte[???];
                bytesRead = _inputStream.Read(compressedPacket, 0, compressedPacket.Length);
                int thisFrameSize = decoder.Decode(compressedPacket, 0, compressedPacket.Length, audioBuffer, 0, frameSize, false);
                Debug.WriteLine("Frame size = " + thisFrameSize);
                _audioTrack.Write(audioBuffer, 0, bytesRead);
            }
            catch (System.Exception)
            {
                bytesRead = 0;
            }
        } while (bytesRead > 0 && _audioTrack.PlayState == PlayState.Playing);

        if (!(_audioTrack.PlayState == PlayState.Stopped))
        {
            RaisePlaybackCompleted(this, new EventArgs());
        }
    }

我的问题是...如果帧大小必须与在压缩（如果我理解正确的话）？

Answer 1

我认为你要求的是一种打包机制。这里真正的问题是，到目前为止，Concentus 仅在原始 Opus 数据包上运行，但没有代码来实际解析数据包所在的容器（.opus 文件实际上是包含 opus 数据流的 Ogg 媒体容器文件）。所以，如果你真的想要 read/write .opus 格式，你必须为 Ogg 文件实现一个 reader/writer，或者等我在 Concentus 包中实际实现一个（抱歉） .

NVorbis 有一个本机 Ogg 解析器，可以为此目的进行修改。或者，如果您不关心与其他程序的兼容性，您可以通过在每个编码的 Opus 数据块之前编写一个 2 字节的数据包长度字段来实现自己的基本分包器。

编辑：因为无论如何我都需要去做，所以我已经开始研究 Oggfile 解析器包，尽管到目前为止只实现了解码器：https://www.nuget.org/packages/Concentus.Oggfile

edit2：Opusfile 编码器现已实现；-)

如何找到正确的缓冲区大小以使用 Concentus 解压缩 Opus 文件

How can I find the correct buffer size for decompressing an Opus file with Concentus

c#

xamarin.android

opus