Add Chunked Audio Clip Store

Util/Audio/Clip/PCMResampler.cs

@@ -0,0 +1,106 @@
+using System;
+using FFmpeg.AutoGen;
+
+namespace ADOFAIRenderer.Util.Audio.Clip;
+
+/// <summary>
+/// Sample rate converter for interleaved 32-bit float PCM (libswresample).
+/// Input and output have the same channel count; only the sample rate changes.
+/// One instance keeps filter state between calls, so consecutive <see cref="Convert"/> calls form one continuous stream.
+/// Reference: https://ffmpeg.org/doxygen/trunk/group__lswr.html
+/// </summary>
+internal sealed unsafe class PCMResampler : IDisposable
+{
+    private SwrContext* _swr;
+    private bool _flushed;
+
+    public int Channels { get; }
+    public int InputRate { get; }
+    public int OutputRate { get; }
+
+    /// <summary>Value of the SwrContext "filter_size" option (filter length per phase in taps at a 1:1 ratio).</summary>
+    public int FilterSize { get; }
+
+    public PCMResampler(int channels, int inputRate, int outputRate)
+    {
+        if (channels <= 0) throw new ArgumentOutOfRangeException(nameof(channels));
+        if (inputRate <= 0) throw new ArgumentOutOfRangeException(nameof(inputRate));
+        if (outputRate <= 0) throw new ArgumentOutOfRangeException(nameof(outputRate));
+
+        Channels = channels;
+        InputRate = inputRate;
+        OutputRate = outputRate;
+
+        AVChannelLayout layout;
+        ffmpeg.av_channel_layout_default(&layout, channels);
+
+        SwrContext* swr = null;
+        var ret = ffmpeg.swr_alloc_set_opts2(
+            &swr,
+            &layout, AVSampleFormat.AV_SAMPLE_FMT_FLT, outputRate,
+            &layout, AVSampleFormat.AV_SAMPLE_FMT_FLT, inputRate,
+            0, null);
+        ffmpeg.av_channel_layout_uninit(&layout);
+        if (ret < 0 || swr == null)
+            throw new InvalidOperationException($"swr_alloc_set_opts2 failed ({ret}).");
+        _swr = swr;
+
+        long filterSize;
+        FilterSize = ffmpeg.av_opt_get_int(_swr, "filter_size", 0, &filterSize) >= 0 ? (int)filterSize : 32;
+
+        Reset();
+    }
+
+    /// <summary>Discards all buffered input and filter history. The next call starts a new stream.</summary>
+    public void Reset()
+    {
+        // swr_init on an initialized context re-initializes it.
+        // Reference: https://ffmpeg.org/doxygen/trunk/group__lswr.html (swr_init, swr_close)
+        var ret = ffmpeg.swr_init(_swr);
+        if (ret < 0)
+            throw new InvalidOperationException($"swr_init failed ({ret}).");
+        _flushed = false;
+    }
+
+    /// <summary>
+    /// Feeds <paramref name="inputFrames"/> frames and writes up to <paramref name="outputCapacity"/> frames.
+    /// Input that does not fit in the output is buffered inside the context and returned by later calls.
+    /// <paramref name="inputFrames"/> may be 0 to take only buffered output.
+    /// </summary>
+    /// <returns>Frames written to <paramref name="output"/>.</returns>
+    public int Convert(float* input, int inputFrames, float* output, int outputCapacity)
+    {
+        if (_flushed) throw new InvalidOperationException("Resampler was flushed. Call Reset first.");
+
+        // swr_convert treats a null input array as a flush request, so a non-null pointer is passed even for 0 frames.
+        float dummy = 0;
+        var inPlane = (byte*)(input != null ? input : &dummy);
+        var outPlane = (byte*)output;
+        var ret = ffmpeg.swr_convert(_swr, &outPlane, outputCapacity, &inPlane, inputFrames);
+        if (ret < 0)
+            throw new InvalidOperationException($"swr_convert failed ({ret}).");
+        return ret;
+    }
+
+    /// <summary>
+    /// Ends the input stream and writes up to <paramref name="outputCapacity"/> remaining frames.
+    /// Call repeatedly until it returns 0. <see cref="Convert"/> is not allowed afterwards until <see cref="Reset"/>.
+    /// </summary>
+    public int Flush(float* output, int outputCapacity)
+    {
+        _flushed = true;
+        var outPlane = (byte*)output;
+        var ret = ffmpeg.swr_convert(_swr, &outPlane, outputCapacity, null, 0);
+        if (ret < 0)
+            throw new InvalidOperationException($"swr_convert (flush) failed ({ret}).");
+        return ret;
+    }
+
+    public void Dispose()
+    {
+        if (_swr == null) return;
+        var swr = _swr;
+        ffmpeg.swr_free(&swr);
+        _swr = null;
+    }
+}