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Use better audio VBR settings

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LAME's VBR mode only has advantage over a certain bitrate range. For very low and very high bitrate, use the ABR mode instead.

aac_at's CVBR mode produces very good quality and is not worse than its TVBR mode in blind testing. Use this mode for convenience.

The ffmpeg native aac encoder will have quality regression with its VBR mode. Always use CBR mode for ffmpeg's native aac encoder.

Signed-off-by: gnattu <gnattuoc@me.com>
This commit is contained in:
gnattu 2024-04-22 21:02:20 +08:00
parent c050abf3e8
commit 78929418cc
2 changed files with 25 additions and 12 deletions
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4
Jellyfin.Api/Controllers/DynamicHlsController.cs
View File

@ -1671,7 +1671,7 @@ public class DynamicHlsController : BaseJellyfinApiController
if (audioBitrate.HasValue && !EncodingHelper.LosslessAudioCodecs.Contains(state.ActualOutputAudioCodec, StringComparison.OrdinalIgnoreCase))
{
var vbrParam = _encodingHelper.GetAudioVbrModeParam(audioCodec, audioBitrate.Value / (audioChannels ?? 2));
var vbrParam = _encodingHelper.GetAudioVbrModeParam(audioCodec, audioBitrate.Value, audioChannels ?? 2);
if (_encodingOptions.EnableAudioVbr && vbrParam is not null)
{
audioTranscodeParams += vbrParam;
@ -1724,7 +1724,7 @@ public class DynamicHlsController : BaseJellyfinApiController
var bitrate = state.OutputAudioBitrate;
if (bitrate.HasValue && !EncodingHelper.LosslessAudioCodecs.Contains(actualOutputAudioCodec, StringComparison.OrdinalIgnoreCase))
{
var vbrParam = _encodingHelper.GetAudioVbrModeParam(audioCodec, bitrate.Value / (channels ?? 2));
var vbrParam = _encodingHelper.GetAudioVbrModeParam(audioCodec, bitrate.Value, channels ?? 2);
if (_encodingOptions.EnableAudioVbr && vbrParam is not null)
{
args += vbrParam;

33
MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs
View File

@ -2586,8 +2586,9 @@ namespace MediaBrowser.Controller.MediaEncoding
return 128000 * (outputAudioChannels ?? audioStream.Channels ?? 2);
}
public string GetAudioVbrModeParam(string encoder, int bitratePerChannel)
public string GetAudioVbrModeParam(string encoder, int bitrate, int channels)
{
var bitratePerChannel = bitrate / channels;
if (string.Equals(encoder, "libfdk_aac", StringComparison.OrdinalIgnoreCase))
{
return " -vbr:a " + bitratePerChannel switch
@ -2602,14 +2603,26 @@ namespace MediaBrowser.Controller.MediaEncoding
if (string.Equals(encoder, "libmp3lame", StringComparison.OrdinalIgnoreCase))
{
return " -qscale:a " + bitratePerChannel switch
// lame's VBR is only good for a certain bitrate range
// For very low and very high bitrate, use abr mode
if (bitratePerChannel is < 122500 and > 48000)
{
< 48000 => "8",
< 64000 => "6",
< 88000 => "4",
< 112000 => "2",
_ => "0"
};
return " -qscale:a " + bitratePerChannel switch
{
< 64000 => "6",
< 88000 => "4",
< 112000 => "2",
_ => "0"
};
}
return " -abr:a 1" + " -b:a " + bitrate;
}
if (string.Equals(encoder, "aac_at", StringComparison.OrdinalIgnoreCase))
{
// aac_at's CVBR mode
return " -aac_at_mode:a 2" + " -b:a " + bitrate;
}
if (string.Equals(encoder, "libvorbis", StringComparison.OrdinalIgnoreCase))
@ -6962,7 +6975,7 @@ namespace MediaBrowser.Controller.MediaEncoding
var bitrate = state.OutputAudioBitrate;
if (bitrate.HasValue && !LosslessAudioCodecs.Contains(codec, StringComparison.OrdinalIgnoreCase))
{
var vbrParam = GetAudioVbrModeParam(codec, bitrate.Value / (channels ?? 2));
var vbrParam = GetAudioVbrModeParam(codec, bitrate.Value, channels ?? 2);
if (encodingOptions.EnableAudioVbr && vbrParam is not null)
{
args += vbrParam;
@ -6993,7 +7006,7 @@ namespace MediaBrowser.Controller.MediaEncoding
if (bitrate.HasValue && !LosslessAudioCodecs.Contains(outputCodec, StringComparison.OrdinalIgnoreCase))
{
var vbrParam = GetAudioVbrModeParam(GetAudioEncoder(state), bitrate.Value / (channels ?? 2));
var vbrParam = GetAudioVbrModeParam(GetAudioEncoder(state), bitrate.Value, channels ?? 2);
if (encodingOptions.EnableAudioVbr && vbrParam is not null)
{
audioTranscodeParams.Add(vbrParam);