| disable-model-invocation | true |
| name | convert-audio-mono |
| description | 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. |
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
- 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.
- 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:
- 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.
