====== ffmpeg - Audio - Audio Channels - Change Audio Channels - Stereo to Mono ======

===== Downmix both channels =====

{{:ffmpeg:audio:audio_channels:audio_channels_-_stereo_to_mono.png?200|}}

<code bash>
ffmpeg -i "input.mkv" -map 0:0 -c:v copy -ac 1 mono.mkv
</code>

<WRAP important>
**WARNING:** Any out of phase stereo will cancel out.

  * **-map 0:0 -c:v copy** to preserve the video stream.

The following filtergraph can be used to bring out of phase stereo in phase prior to downmixing:

<code bash>
-af "asplit[a],aphasemeter=video=0,ametadata=select:key=lavfi.aphasemeter.phase:value=-0.005:function=less,pan=1c|c0=c0,aresample=async=1:first_pts=0,[a]amix"
</code>

</WRAP>

----

===== Choose a specific channel =====

{{:ffmpeg:audio:audio_channels:audio_channels_-_stereo_to_mono_-_exclude.png?200|}}

==== ...using the channelsplit audio filter ====

<code bash>
ffmpeg -i stereo.wav -filter_complex "[0:a]channelsplit=channel_layout=stereo:channels=FR[right]" -map "[right]" front_right.wav
</code>

<WRAP info>
**NOTE:**  This uses the [[https://ffmpeg.org/ffmpeg-filters.html#channelsplit|channelsplit]] audio filter to include only the right channel.

  * If you only want the left channel use **FL** instead of **FR**.

  * For a list of channel names, run <code bash>ffmpeg -layouts</code>
</WRAP>

----

==== ...using the pan audio filter ====

<code bash>
ffmpeg -i "input.mkv" -map 0:0 -c:v copy -af "pan=mono|c0=c1" "mono.mkv"
</code>

<WRAP info>
**NOTE:**  This uses the [[https://ffmpeg.org/ffmpeg-filters.html#pan|pan]] audio filter to include only the right channel.

  * **-map 0:0 -c:v copy** to preserve the video stream.

  * Alternatively, you could use **c0=FR** instead.

  * If you only want the left channel, use **c0=c0** or **c0=FL** instead.
</WRAP>




----

===== References =====

https://trac.ffmpeg.org/wiki/AudioChannelManipulation#stereomonostream

https://ffmpeg.org/ffmpeg-filters.html#channelsplit

https://ffmpeg.org/ffmpeg-filters.html#pan