SHA256
107 lines
4.1 KiB
C#
107 lines
4.1 KiB
C#
using System;
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using FFmpeg.AutoGen;
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namespace ADOFAIRenderer.Util.Audio.Clip;
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/// <summary>
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/// Sample rate converter for interleaved 32-bit float PCM (libswresample).
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/// Input and output have the same channel count; only the sample rate changes.
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/// One instance keeps filter state between calls, so consecutive <see cref="Convert"/> calls form one continuous stream.
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/// Reference: https://ffmpeg.org/doxygen/trunk/group__lswr.html
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/// </summary>
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internal sealed unsafe class PCMResampler : IDisposable
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{
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private SwrContext* _swr;
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private bool _flushed;
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public int Channels { get; }
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public int InputRate { get; }
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public int OutputRate { get; }
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/// <summary>Value of the SwrContext "filter_size" option (filter length per phase in taps at a 1:1 ratio).</summary>
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public int FilterSize { get; }
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public PCMResampler(int channels, int inputRate, int outputRate)
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{
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if (channels <= 0) throw new ArgumentOutOfRangeException(nameof(channels));
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if (inputRate <= 0) throw new ArgumentOutOfRangeException(nameof(inputRate));
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if (outputRate <= 0) throw new ArgumentOutOfRangeException(nameof(outputRate));
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Channels = channels;
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InputRate = inputRate;
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OutputRate = outputRate;
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AVChannelLayout layout;
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ffmpeg.av_channel_layout_default(&layout, channels);
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SwrContext* swr = null;
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var ret = ffmpeg.swr_alloc_set_opts2(
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&swr,
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&layout, AVSampleFormat.AV_SAMPLE_FMT_FLT, outputRate,
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&layout, AVSampleFormat.AV_SAMPLE_FMT_FLT, inputRate,
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0, null);
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ffmpeg.av_channel_layout_uninit(&layout);
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if (ret < 0 || swr == null)
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throw new InvalidOperationException($"swr_alloc_set_opts2 failed ({ret}).");
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_swr = swr;
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long filterSize;
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FilterSize = ffmpeg.av_opt_get_int(_swr, "filter_size", 0, &filterSize) >= 0 ? (int)filterSize : 32;
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Reset();
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}
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/// <summary>Discards all buffered input and filter history. The next call starts a new stream.</summary>
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public void Reset()
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{
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// swr_init on an initialized context re-initializes it.
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// Reference: https://ffmpeg.org/doxygen/trunk/group__lswr.html (swr_init, swr_close)
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var ret = ffmpeg.swr_init(_swr);
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if (ret < 0)
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throw new InvalidOperationException($"swr_init failed ({ret}).");
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_flushed = false;
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}
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/// <summary>
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/// Feeds <paramref name="inputFrames"/> frames and writes up to <paramref name="outputCapacity"/> frames.
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/// Input that does not fit in the output is buffered inside the context and returned by later calls.
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/// <paramref name="inputFrames"/> may be 0 to take only buffered output.
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/// </summary>
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/// <returns>Frames written to <paramref name="output"/>.</returns>
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public int Convert(float* input, int inputFrames, float* output, int outputCapacity)
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{
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if (_flushed) throw new InvalidOperationException("Resampler was flushed. Call Reset first.");
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// swr_convert treats a null input array as a flush request, so a non-null pointer is passed even for 0 frames.
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float dummy = 0;
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var inPlane = (byte*)(input != null ? input : &dummy);
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var outPlane = (byte*)output;
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var ret = ffmpeg.swr_convert(_swr, &outPlane, outputCapacity, &inPlane, inputFrames);
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if (ret < 0)
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throw new InvalidOperationException($"swr_convert failed ({ret}).");
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return ret;
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}
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/// <summary>
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/// Ends the input stream and writes up to <paramref name="outputCapacity"/> remaining frames.
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/// Call repeatedly until it returns 0. <see cref="Convert"/> is not allowed afterwards until <see cref="Reset"/>.
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/// </summary>
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public int Flush(float* output, int outputCapacity)
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{
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_flushed = true;
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var outPlane = (byte*)output;
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var ret = ffmpeg.swr_convert(_swr, &outPlane, outputCapacity, null, 0);
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if (ret < 0)
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throw new InvalidOperationException($"swr_convert (flush) failed ({ret}).");
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return ret;
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}
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public void Dispose()
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{
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if (_swr == null) return;
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var swr = _swr;
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ffmpeg.swr_free(&swr);
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_swr = null;
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}
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}
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