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convert-audio-mono

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Use when the user wants to convert a video or audio file's stereo audio to mono, or fix audio that only plays in one ear.

QUICK START

How to use this skill

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  3. Review the proposed files and risks before you approve installation.
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Source SKILL.md: https://github.com/jackfranklin/dotfiles/blob/HEAD/claude/skills/convert-audio-mono/SKILL.md

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Convert Audio to Mono

Overview

This skill converts the stereo audio channel of a media file (typically video or audio) to mono. It optimizes the process by copying the video stream without re-encoding to preserve video quality, and handles silent channels by extracting the active channel rather than a simple downmix.

When to Use

Use when a video or audio file's sound plays in only one ear/channel, or when a mono mix is requested.

Core Pattern

  1. Analyze Channel Volumes: Run ffmpeg -i <input> -filter_complex "[0:a]astats=metadata=1" -f null - to identify the peak and RMS volume of each channel. Note: Do not use reset=1 in the filter, as it resets stats per frame.
  2. Determine Extraction Strategy:
    • If one channel is silent (volume ~ -90 dB or less) and the other has sound, isolate the active channel to avoid a 6 dB volume drop from normal averaging:
      • Left channel only: -af "pan=mono|c0=c0" (or FL)
      • Right channel only: -af "pan=mono|c0=c1" (or FR)
    • If both channels have active sound, use standard downmixing:
      • -ac 1
  3. Execute Conversion: Run ffmpeg, copying the video stream to save time and preserve quality: ffmpeg -i <input> -c:v copy -af "<filter>" -c:a aac -b:a 256k <output>

Common Mistakes

  • Re-encoding video: Re-encoding the video stream degrades quality and takes significant time. Always use -c:v copy.
  • Averaging silent channels: A simple -ac 1 downmix of a one-eared track averages it with silence, dropping the overall volume by 6 dB. Always analyze first and use the pan filter for single-channel isolation.