Resize a video with FFmpeg for Mastodon

How to resize a video with FFmpeg before uploading it to Mastodon to comply its resolution and size restrictions.

© 2022 Paolo Melchiorre CC BY-SA “Noah Alorwu warming up the audience (with Mauro Gaspari) at Ubuntu Summit 2022 in Prague (Czech Republic)”

TL;DR¶

$ ffmpeg -i input.mp4 -vf scale=1920:-1 -vcodec libx265 -crf 24 output.mp4

Premise¶

Last week I attended the Ubuntu Summit 2022 in Prague (Czech Republic) and as for other conferences I shared some moments live on Mastodon.

At the start of day three Noah Alorwu animated the audience with a fun little dance which I filmed, but when I tried to upload the file to a post, Mastodon gave me an error message.

Media restrictions¶

Although not well documented I have found the restrictions that Mastodon applies to videos which I try to summarize below:

• maximum size: 40 megabytes
• maximum resolution: 1920 x 1200 px
• maximum frame rate: 60 fps
• allowed extensions: .webm .mp4 .m4v .mov

FFmpeg command¶

The video in mp4 format I recorded was only 12 seconds long but had a size of 65 megabytes and a resolution of 3840 x 2160 pixels.

To be able to upload it to Mastodon I had to reduce the last two parameters using FFmpeg as follows:

$ ffmpeg -i input.mp4 -vf scale=1920:-1 -vcodec libx265 -crf 24 output.mp4

Mastodon toot¶

The resulting file from the conversion had a size of 12 megabytes and a resolution of 1920 x 1080 pixels which I was able to upload to Mastodon.

Your browser doesn’t support video. Here is a link to the video instead. https://fosstodon.org/@paulox/109313241179228985

References¶

To learn more, you can read:

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