voice-cat/tests/VoiceCat.Tests/CodecTests.cs

using VoiceCat.Codec;

namespace VoiceCat.Tests;

public sealed class CodecTests
{
    public static IEnumerable<object[]> Formats()
    {
        foreach (int rate in new[] { 8000, 12000, 16000, 24000, 48000 })
        foreach (int channels in new[] { 1, 2 })
        foreach (int duration in new[] { 10, 20, 40, 60 })
            yield return [rate, channels, duration];
    }

    [Theory]
    [MemberData(nameof(Formats))]
    public void RoundTripAndLossConcealment(int sampleRate, int channels, int duration)
    {
        var options = new OpusOptions { SampleRate = sampleRate, Channels = channels, FrameDurationMilliseconds = duration, Bitrate = 64000 };
        using var encoder = new OpusEncoder(options);
        using var decoder = new OpusDecoder(sampleRate, channels);
        short[] input = new short[options.SamplesPerChannel * channels];
        short[] output = new short[input.Length];
        byte[] packet = new byte[4000];
        for (int frame = 0; frame < 12; frame++)
        {
            FillTone(input, options.SamplesPerChannel, channels, sampleRate, frame);
            int bytes = encoder.Encode(input, packet);
            Assert.InRange(bytes, 1, packet.Length);
            Assert.Equal(options.SamplesPerChannel, decoder.Decode(packet.AsSpan(0, bytes), output, options.SamplesPerChannel));
        }
        double rms = Rms(output);
        Assert.InRange(rms, 2000, 12000);
        Assert.Equal(options.SamplesPerChannel, decoder.Decode([], output, options.SamplesPerChannel));
        Assert.True(Rms(output) > 100);
    }

    [Fact]
    public void RejectsInvalidStorageAndOptionsBeforeNativeCalls()
    {
        Assert.Throws<ArgumentOutOfRangeException>(() => new OpusEncoder(new() { Channels = 3 }));
        Assert.Throws<ArgumentOutOfRangeException>(() => new OpusEncoder(new() { FrameDurationMilliseconds = 30 }));
        using var encoder = new OpusEncoder();
        using var decoder = new OpusDecoder();
        Assert.Throws<ArgumentException>(() => encoder.Encode(new short[959], new byte[4000]));
        Assert.Throws<ArgumentException>(() => decoder.Decode([], new short[959], 960));
        encoder.Dispose();
        Assert.Throws<ObjectDisposedException>(() => encoder.Encode(new short[960], new byte[4000]));
    }

    [Fact]
    public void DredIsExplicitlySupportedOrRejected()
    {
        using var probe = new OpusEncoder();
        Assert.Contains("libopus", OpusEncoder.Version);
        if (!probe.SupportsDeepRedundancy)
        {
            Assert.Throws<NotSupportedException>(() => new OpusEncoder(new() { DeepRedundancy = true }));
            Assert.Throws<NotSupportedException>(() => new OpusDeepRedundancy());
            return;
        }
        VerifyDredRecovery(new() { DeepRedundancy = true, ExpectedPacketLossPercent = 20, Bitrate = 64000 });
    }

    [Theory]
    [MemberData(nameof(Formats))]
    public void DredRecoversDroppedFrames(int sampleRate, int channels, int duration)
    {
        using var probe = new OpusEncoder();
        Assert.True(probe.SupportsDeepRedundancy, "Build native bindings with scripts/build-native.ps1 for DRED recovery tests.");
        if (sampleRate < 16000)
            Assert.Throws<NotSupportedException>(() => new OpusEncoder(new() { SampleRate = sampleRate, DeepRedundancy = true }));
        VerifyDredRecovery(new() { SampleRate = sampleRate, Channels = channels,
            FrameDurationMilliseconds = duration, DeepRedundancy = true, ExpectedPacketLossPercent = 20, Bitrate = 64000 });
    }

    private static void VerifyDredRecovery(OpusOptions options)
    {
        // The pinned encoder cannot emit DRED at 8/12 kHz; packets can still be decoded at those rates.
        var encoderOptions = options with { SampleRate = Math.Max(16000, options.SampleRate) };
        using var encoder = new OpusEncoder(encoderOptions);
        using var decoder = new OpusDecoder(options.SampleRate, options.Channels);
        using var recovery = new OpusDeepRedundancy();
        short[] input = new short[encoderOptions.SamplesPerChannel * options.Channels];
        short[] output = new short[options.SamplesPerChannel * options.Channels];
        byte[] packet = new byte[4000];
        bool missing = false;
        int recovered = 0;
        for (int frame = 0; frame < 40; frame++)
        {
            FillTone(input, encoderOptions.SamplesPerChannel, options.Channels, encoderOptions.SampleRate, frame);
            int bytes = encoder.Encode(input, packet);
            if (missing)
            {
                Assert.True(recovery.TryRecover(decoder, packet.AsSpan(0, bytes), output, options.SamplesPerChannel));
                Assert.True(Rms(output) > 10);
                recovered++;
                missing = false;
            }
            if (frame > 20 && frame % 5 == 0)
            {
                missing = true;
                continue;
            }
            decoder.Decode(packet.AsSpan(0, bytes), output, options.SamplesPerChannel);
        }
        Assert.Equal(3, recovered);
    }

    internal static void FillTone(Span<short> pcm, int samples, int channels, int rate, int frame)
    {
        for (int i = 0; i < samples; i++)
        for (int channel = 0; channel < channels; channel++)
            pcm[i * channels + channel] = (short)(8000 * Math.Sin(2 * Math.PI * (440 + 220 * channel) * (frame * samples + i) / rate));
    }

    internal static double Rms(ReadOnlySpan<short> pcm)
    {
        double sum = 0;
        foreach (short value in pcm) sum += (double)value * value;
        return Math.Sqrt(sum / pcm.Length);
    }
}