MkvOpusEnc

A powerful PowerShell script for advanced audio track processing in MKV files. This script intelligently re-encodes or remuxes audio tracks based on their codec, while preserving all video, subtitle, attachment, and metadata information.

It includes a flexible downmixing feature to convert multi-channel surround sound into a dialogue-focused stereo track, perfect for "night mode" listening or playback on stereo devices.

Key Features

• Selective Re-encoding: Automatically re-encodes common high-bitrate codecs like DTS, AC3, E-AC3, and FLAC into the efficient Opus format.
• Lossless Remuxing: Preserves audio quality by remuxing (copying) tracks that are already in a modern format like AAC or Opus.
• Full Metadata Preservation: Carefully reads and re-applies all critical metadata, ensuring nothing is lost:
  • Video, Subtitle, and Font Attachments are all carried over.
  • Audio Track Titles (e.g., "Commentary by Director") are preserved.
  • Audio Track Language tags are preserved.
  • Audio Delay (A/V Sync) is read accurately and re-applied to maintain perfect synchronization.
• Optional Downmixing: A -Downmix switch transforms the script's behavior:
  • Standard Mode: Preserves the original channel layout (e.g., 5.1 DTS becomes 5.1 Opus).
  • Downmix Mode: Converts 5.1 or 7.1 surround sound into a high-quality stereo track.
• High-Quality Downmix Formulas: Uses specific, fine-tuned ffmpeg pan filters for downmixing, including a "dialogue boost" formula for clear speech.
• Cross-Platform: Fully compatible with PowerShell 7 on Windows and Linux.
• Clean Operation: Creates and automatically cleans up a temporary directory for all intermediate files.

Requirements

1. PowerShell 7+ (for cross-platform compatibility)
2. FFmpeg: For audio extraction and downmixing.
3. MKVToolNix: For reading container data and final muxing (mkvmerge).
4. SoX (Sound eXchange): For audio normalization.
5. opus-tools: For Opus encoding (opusenc).
6. MediaInfo: For accurate audio delay detection.

Installation

First, ensure you have PowerShell 7 or newer installed. Then, install the required command-line tools. They must be available in your system's PATH.

Windows (using Chocolatey)

choco install ffmpeg mkvtoolnix sox opus-tools mediainfo

Linux (Debian / Ubuntu)

sudo apt-get update
sudo apt-get install ffmpeg mkvtoolnix sox opus-tools mediainfo

Linux (Arch Linux)

sudo pacman -Syu ffmpeg mkvtoolnix-cli sox opus-tools mediainfo

(Note: on Arch, the package is mkvtoolnix-cli)

Usage

The script is run from the command line, providing an input file, an output file, and an optional switch to control downmixing.

./MkvOpusEnc.ps1 -InputFile <path> -OutputFile <path> [-Downmix]

Parameters

• -InputFile <string>
  • (Required) The full path to the source MKV file.
• -OutputFile <string>
  • (Required) The full path for the processed output MKV file.
• -Downmix
  • (Optional Switch) If this flag is present, any 5.1 or 7.1 audio tracks that are being re-encoded will be downmixed to stereo. If omitted, their original channel layout will be preserved.

Examples

Example 1: Standard Mode (Preserving Channels)

This command will re-encode a 5.1 DTS track into a 5.1 Opus track.

./MkvOpusEnc.ps1 -InputFile "C:\Movies\MyMovie.mkv" -OutputFile "C:\Movies\MyMovie-Opus.mkv"

Example 2: Downmix Mode (Creating Stereo)

This command will re-encode a 5.1 DTS track into a stereo Opus track using the "dialogue boost" formula.

./MkvOpusEnc.ps1 -InputFile "C:\Movies\MyMovie.mkv" -OutputFile "C:\Movies\MyMovie-Stereo.mkv" -Downmix

Example 3: Batch Mode

This command will re-encode multiple files to Opus.

foreach ($file in gci *.mkv ) {$new = $file.BaseName + "_opus" + $file.Extension ; MkvOpusEnc.ps1 -InputFile $file -OutputFile $new }