75 lines
4.9 KiB
C#
75 lines
4.9 KiB
C#
using System.Collections.Generic;
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using MediaBrowser.Model.Entities;
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namespace MediaBrowser.Controller.MediaEncoding;
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/// <summary>
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/// Describes the downmix algorithms capabilities.
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/// </summary>
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public static class DownMixAlgorithmsHelper
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{
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/// <summary>
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/// The filter string of the DownMixStereoAlgorithms.
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/// The index is the tuple of (algorithm, layout).
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/// </summary>
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public static readonly Dictionary<(DownMixStereoAlgorithms, string), string> AlgorithmFilterStrings = new()
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{
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{ (DownMixStereoAlgorithms.Dave750, "5.1"), "pan=stereo|c0=0.5*c2+0.707*c0+0.707*c4+0.5*c3|c1=0.5*c2+0.707*c1+0.707*c5+0.5*c3" },
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// Use AC-4 algorithm to downmix 7.1 inputs to 5.1 first
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{ (DownMixStereoAlgorithms.Dave750, "7.1"), "pan=5.1(side)|c0=c0|c1=c1|c2=c2|c3=c3|c4=0.707*c4+0.707*c6|c5=0.707*c5+0.707*c7,pan=stereo|c0=0.5*c2+0.707*c0+0.707*c4+0.5*c3|c1=0.5*c2+0.707*c1+0.707*c5+0.5*c3" },
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{ (DownMixStereoAlgorithms.NightmodeDialogue, "5.1"), "pan=stereo|c0=c2+0.30*c0+0.30*c4|c1=c2+0.30*c1+0.30*c5" },
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// Use AC-4 algorithm to downmix 7.1 inputs to 5.1 first
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{ (DownMixStereoAlgorithms.NightmodeDialogue, "7.1"), "pan=5.1(side)|c0=c0|c1=c1|c2=c2|c3=c3|c4=0.707*c4+0.707*c6|c5=0.707*c5+0.707*c7,pan=stereo|c0=c2+0.30*c0+0.30*c4|c1=c2+0.30*c1+0.30*c5" },
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{ (DownMixStereoAlgorithms.Rfc7845, "3.0"), "pan=stereo|c0=0.414214*c2+0.585786*c0|c1=0.414214*c2+0.585786*c1" },
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{ (DownMixStereoAlgorithms.Rfc7845, "quad"), "pan=stereo|c0=0.422650*c0+0.366025*c2+0.211325*c3|c1=0.422650*c1+0.366025*c3+0.211325*c2" },
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{ (DownMixStereoAlgorithms.Rfc7845, "5.0"), "pan=stereo|c0=0.460186*c2+0.650802*c0+0.563611*c3+0.325401*c4|c1=0.460186*c2+0.650802*c1+0.563611*c4+0.325401*c3" },
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{ (DownMixStereoAlgorithms.Rfc7845, "5.1"), "pan=stereo|c0=0.374107*c2+0.529067*c0+0.458186*c4+0.264534*c5+0.374107*c3|c1=0.374107*c2+0.529067*c1+0.458186*c5+0.264534*c4+0.374107*c3" },
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{ (DownMixStereoAlgorithms.Rfc7845, "6.1"), "pan=stereo|c0=0.321953*c2+0.455310*c0+0.394310*c5+0.227655*c6+0.278819*c4+0.321953*c3|c1=0.321953*c2+0.455310*c1+0.394310*c6+0.227655*c5+0.278819*c4+0.321953*c3" },
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{ (DownMixStereoAlgorithms.Rfc7845, "7.1"), "pan=stereo|c0=0.274804*c2+0.388631*c0+0.336565*c6+0.194316*c7+0.336565*c4+0.194316*c5+0.274804*c3|c1=0.274804*c2+0.388631*c1+0.336565*c7+0.194316*c6+0.336565*c5+0.194316*c4+0.274804*c3" },
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{ (DownMixStereoAlgorithms.Ac4, "3.0"), "pan=stereo|c0=c0+0.707*c2|c1=c1+0.707*c2" },
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{ (DownMixStereoAlgorithms.Ac4, "5.0"), "pan=stereo|c0=c0+0.707*c2+0.707*c3|c1=c1+0.707*c2+0.707*c4" },
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{ (DownMixStereoAlgorithms.Ac4, "5.1"), "pan=stereo|c0=c0+0.707*c2+0.707*c4|c1=c1+0.707*c2+0.707*c5" },
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{ (DownMixStereoAlgorithms.Ac4, "7.0"), "pan=5.0(side)|c0=c0|c1=c1|c2=c2|c3=0.707*c3+0.707*c5|c4=0.707*c4+0.707*c6,pan=stereo|c0=c0+0.707*c2+0.707*c3|c1=c1+0.707*c2+0.707*c4" },
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{ (DownMixStereoAlgorithms.Ac4, "7.1"), "pan=5.1(side)|c0=c0|c1=c1|c2=c2|c3=c3|c4=0.707*c4+0.707*c6|c5=0.707*c5+0.707*c7,pan=stereo|c0=c0+0.707*c2+0.707*c4|c1=c1+0.707*c2+0.707*c5" },
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};
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/// <summary>
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/// Get the audio channel layout string from the audio stream
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/// If the input audio string does not have a valid layout string, guess from channel count.
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/// </summary>
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/// <param name="audioStream">The audio stream to get layout.</param>
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/// <returns>Channel Layout string.</returns>
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public static string InferChannelLayout(MediaStream audioStream)
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{
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if (!string.IsNullOrWhiteSpace(audioStream.ChannelLayout))
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{
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// Note: BDMVs do not derive this string from ffmpeg, which would cause ambiguity with 4-channel audio
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// "quad" => 2 front and 2 rear, "4.0" => 3 front and 1 rear
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// BDMV will always use "4.0" in this case
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// Because the quad layout is super rare in BDs, we will use "4.0" as is here
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return audioStream.ChannelLayout;
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}
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if (audioStream.Channels is null)
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{
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return string.Empty;
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}
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// When we don't have definitive channel layout, we have to guess from the channel count
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// Guessing is not always correct, but for most videos we don't have to guess like this as the definitive layout is recorded during scan
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var inferredLayout = audioStream.Channels.Value switch
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{
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1 => "mono",
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2 => "stereo",
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3 => "2.1", // Could also be 3.0, prefer 2.1
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4 => "4.0", // Could also be quad (with rear left and rear right) and 3.1 with LFE. prefer 4.0 with front center and back center
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5 => "5.0",
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6 => "5.1", // Could also be 6.0 or hexagonal, prefer 5.1
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7 => "6.1", // Could also be 7.0, prefer 6.1
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8 => "7.1", // Could also be 8.0, prefer 7.1
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_ => string.Empty // Return empty string for not supported layout
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};
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return inferredLayout;
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}
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}
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