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Merge pull request #18195 from Shadowghost/fix/18194-audio-downmix-filter

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Apply stereo downmix filter consistently to progressive audio transcodes
This commit is contained in:
Cody Robibero
2026-09-27 15:29:06 -04:00
committed by GitHub
parent 3e27c7ef7f ba256d15dc
commit 4d99715770
2 changed files with 70 additions and 1 deletions
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MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs
+10 -1
View File
@@ -7832,7 +7832,9 @@ namespace MediaBrowser.Controller.MediaEncoding
var channels = state.OutputAudioChannels;
var useDownMixAlgorithm = state.AudioStream is not null
// Must match the condition under which GetAudioFilterParam emits the downmix filter.
var useDownMixAlgorithm = channels == 2
&& state.AudioStream?.Channels > 2
&& DownMixAlgorithmsHelper.AlgorithmFilterStrings.ContainsKey((encodingOptions.DownMixStereoAlgorithm, DownMixAlgorithmsHelper.InferChannelLayout(state.AudioStream)));
if (channels.HasValue && !useDownMixAlgorithm)
@@ -7927,6 +7929,13 @@ namespace MediaBrowser.Controller.MediaEncoding
audioTranscodeParams.Add("-ar " + sampleRateValue.ToString(CultureInfo.InvariantCulture));
}
// Without the downmix filter, -ac 2 alone drops the LFE channel.
var audioFilterParam = GetAudioFilterParam(state, encodingOptions);
if (!string.IsNullOrEmpty(audioFilterParam))
{
audioTranscodeParams.Add(audioFilterParam.TrimStart());
}
// Copy the movflags from GetProgressiveVideoFullCommandLine
// See #9248 and the associated PR for why this is needed
if (_mp4ContainerNames.Contains(state.OutputContainer))
tests/Jellyfin.Controller.Tests/MediaEncoding/EncodingHelperTests.cs
+60
View File
@@ -261,6 +261,66 @@ public class EncodingHelperTests
Assert.Contains("-ar 48000", args, StringComparison.Ordinal);
}
[Fact]
public void GetProgressiveAudioFullCommandLine_StereoDownmix_AppliesDownMixAlgorithm()
{
// Issue #18194: -ac 2 alone drops the LFE channel, the configured downmix filter must be applied.
var state = BuildAudioState("aac", 48000);
state.AudioStream.Channels = 6;
state.AudioStream.ChannelLayout = "5.1";
state.OutputAudioChannels = 2;
var options = new EncodingOptions { DownMixStereoAlgorithm = DownMixStereoAlgorithms.Dave750, DownMixAudioBoost = 1 };
var args = CreateHelper().GetProgressiveAudioFullCommandLine(state, options, "/tmp/out");
Assert.Contains(
"-af \"" + DownMixAlgorithmsHelper.AlgorithmFilterStrings[(DownMixStereoAlgorithms.Dave750, "5.1")] + "\"",
args,
StringComparison.Ordinal);
}
[Fact]
public void GetProgressiveAudioFullCommandLine_NoDownmix_EmitsNoAudioFilter()
{
var state = BuildAudioState("aac", 48000);
state.AudioStream.Channels = 2;
state.OutputAudioChannels = 2;
var options = new EncodingOptions { DownMixStereoAlgorithm = DownMixStereoAlgorithms.Dave750 };
var args = CreateHelper().GetProgressiveAudioFullCommandLine(state, options, "/tmp/out");
Assert.DoesNotContain("-af", args, StringComparison.Ordinal);
}
[Theory]
[InlineData(1)]
[InlineData(6)]
public void GetProgressiveVideoAudioArguments_NonStereoOutput_KeepsChannelCount(int outputChannels)
{
// The downmix filter only applies to stereo output, so -ac must not be dropped otherwise.
var state = BuildAudioState("aac", 48000);
state.AudioStream.Channels = 6;
state.AudioStream.ChannelLayout = "5.1";
state.OutputAudioChannels = outputChannels;
var options = new EncodingOptions { DownMixStereoAlgorithm = DownMixStereoAlgorithms.Dave750 };
var args = CreateHelper().GetProgressiveVideoAudioArguments(state, options);
Assert.Contains("-ac " + outputChannels, args, StringComparison.Ordinal);
Assert.DoesNotContain("pan=", args, StringComparison.Ordinal);
}
[Fact]
public void GetProgressiveVideoAudioArguments_StereoDownmix_UsesFilterInsteadOfChannelCount()
{
var state = BuildAudioState("aac", 48000);
state.AudioStream.Channels = 6;
state.AudioStream.ChannelLayout = "5.1";
state.OutputAudioChannels = 2;
var options = new EncodingOptions { DownMixStereoAlgorithm = DownMixStereoAlgorithms.Dave750 };
var args = CreateHelper().GetProgressiveVideoAudioArguments(state, options);
Assert.DoesNotContain("-ac ", args, StringComparison.Ordinal);
Assert.Contains("pan=stereo", args, StringComparison.Ordinal);
}
private static EncodingJobInfo BuildAudioState(string audioCodec, int requestedSampleRate, string? outputContainer = null)
{
var audio = new MediaStream { Index = 0, Type = MediaStreamType.Audio, Codec = "flac", SampleRate = 96000 };