TL;DR: ffmpeg -i stereo.mov -codec:v copy -af pan="mono| c0=FL" mono.mov
QuickTime doesn’t let you select the channel for an input source, so if you have a standard mono mic connected to a multi-channel audio interface, then the recording you export from QuickTime will end up with the audio only on the left channel, and nothing on the right channel.
Professional video editing tools would make it easy to fix that, but I’m just using iMovie. Neither iMovie 9 or 10 will let you fix it in the project itself, but iMovie 9 will let you export via QuickTime with the audio set to mono.
I can’t use v9, though, because it severely degrades the video quality during import. iMovie 10 fixes the video quality issue, but it removed the export-via-QuickTime feature, so I’m still stuck with the mono audio problem.
One possible solution that sounded promising was using Soundflower to make an aggregate device, so that QuickTime could use it as the audio source, but I couldn’t get that working. The only other thing that seems like it would work would be to export the audio to a DAW like Audacity, convert it to mono, and then import that into iMovie as a separate track. That would be a big hassle for every project, though.
Luckily, there’s a much better solution. After exporting the recording from QuickTime, you can just use ffmpeg to copy the left channel to the right one:
ffmpeg -i stereo.mov -codec:v copy -af pan="mono| c0=FL" mono.mov
Note: On some systems you may need to use a : instead of | in that command.
If you want an alias to do it quickly, you can add this to your .bashrc:
Then you can just run qtmono foo.mov and it’ll output foo-mono.mov.
Lifesaver! Thanks a ton for this. Had exported a video from iMovie, only to have a single channel of audio. This took seconds, instead of me having to export the audio, fix it, re-import and re-render the video.
Appreciate the post!
Awesome! I noted that the syntax appears to have changed a bit, so instead of
mono: c0=FL, you need to usemono| c0=FLwith a pipe instead of the colon.Apart from this, you just saved me hours and hours of work.
Same QT problem using Scarlett and I’ve never used the terminal before. I just successfully converted a stereo QT recording to mono using your FFMPEG directions (also confirmed use syntax
mono| c0=FLnotmono: c0=FL).I feel so powerful. Now I’m going to hack that greedy companies mainframe…
Absolute lifesaver. Great article.
How exactly do I go about this?
Fantastic. Took me about 5 minutes including the brew install of ffmpeg.
I added this to my
~/.bash_profileand I can now do
tomono infile.mov outfile.movnote that the
:has been deprecated and|is used instead.Thanks for the tip!
In my case, I wanted to merge the left and right channels into one mono channel (since the first half of the recording contained only the left channel and the second half contained only the right channel). So the following command worked for me:
$ ffmpeg -i stereo.mov -codec:v copy -ac 1 mono.movThis didn’t work for me when trying to recover the audio on an ipad screen recording, but this article at least clued me in that my issue was a stereo recording with one silent audio channel being played back as mono. I finally found a solution that worked for me to select the right channel using the handbrake solution at the end of this write-up https://khalil-shreateh.com/khalil.shtml/computer/12056-solution-no-sound-when-sending-ios-11-screen-recordings.html
If useful – I solved the ‘soundflower’ fix with Loopback and AudioHijack. Created a standard pass-thru in Loopback and named it Mono_mic. In Audiohijack create a session that is your input device (in my case Scarlett 2i2) Add the Channels effect block and set it to mono. Add Output device and set to your Loopback Pass-thru (in my case ‘mono_mic’) Start that session. In Quicktime or Filmora or where ever, select the Loopback device (mono_mic) as Input. Sorted :)
you are an absolute life saver. I tried so many options including the audacity route but because it is a church service (most mics are mono), it took forever and only to find that the audio and video are out of sync. This just took 30 secs! i couldn’t believe it. It took me a while to figure out FFmpeg but I needed some command prompt navigation, cd to the desktop, ./FFmpeg in its command prompt and I was off and away! Fantastic! Thank you :)
Please help – can you explain exactly what to do? step by step? Thanks
Can you please explain, step by step, what is the procedure of converting a single channel recording (with or without video) on quicktime – to mono?
Thanks
This is very helpful. Thank you very much. I have been struggling a lot to get this done without opening garageband etc.
I noticed that this overwrite the orignal mov metadata with a new one from when the conversion was done. For example creation date etc are regenerated. Do you know if there is way to copy over the original metadata while doing this?
This worked well beside I need find a way to make sure that the creation date of video and other metadata remains in new video. I made this an Automator Script on mac so I can right click on one or multiple video and do a “Quick Action” to just convert it in Finder itself.
I followed this youtube video and replaced the command to with the one in this tutorial.
https://www.youtube.com/watch?v=C1kSS0welHs
Ok so I even got too lazy to do this Quick action over and over again. So I got a “1 XLR Female to 2 XLR Male Patch Y Cable Balanced Microphone Splitter Cord Audio Adaptor” from Amazon and then just connected my microphone through it.
In 2024, on Sonoma:
Error applying option ‘c0’ to filter ‘pan’: Option not found
Error opening output file IntegratedClockinPHP74-mono.mov.
Error opening output files: Option not found