Mastodon video size
1920 × 1080px
Aspect ratio
16:9
Export Mastodon video at 1920 × 1080 px (16:9) as H.264 MP4 — default servers cap files around 99 MB, with no fixed length limit.
Last verified June 2026
Mastodon’s video rules are refreshingly simple and, true to the platform, server-configurable: default-configured instances accept MP4, M4V, MOV, or WebM up to roughly 99 MB, with no hard runtime limit — the file-size cap is the real constraint. The server transcodes uploads to streaming-friendly H.264 MP4, so a clean 1080p export at a moderate bitrate is the professional move: it survives transcoding well and stays small enough to leave room for length.
| Variant | Dimensions | Ratio |
|---|---|---|
| Landscape (recommended) | 1920 × 1080 pxFits timeline players in the official and third-party apps. | 16:9 |
| Vertical | 1080 × 1920 pxDisplays inside the post card, not full-screen — captions need to be larger. | 9:16 |
| Square | 1080 × 1080 px | 1:1 |
| Lighter export | 1280 × 720 pxBuys roughly double the runtime inside the ~99 MB default cap. | 16:9 |
Players overlay controls along the bottom of the video card, so keep captions and essential action out of the bottom ~15%. Since the file-size cap is the binding constraint, treat resolution and length as a trade: a 1080p export at 8 Mbps fits about a minute and a half under 99 MB, while 720p at 4 Mbps fits roughly three minutes. Decide which the content needs before exporting, not after a rejected upload.
The 99 MB default is generous for short clips and tight for long ones, so work backwards: target file size = bitrate × duration. For demos and clips under 90 seconds, 1080p at 8 Mbps is comfortable; for longer talks or screencasts, drop to 720p at 4 Mbps and the math opens up. A two-pass H.264 encode squeezes noticeably more quality into the same megabytes.
Mastodon’s accessibility culture covers video too — the media-description field accepts a summary of what the video shows, and the audience genuinely reads and rewards it. Pair it with burned-in captions (there’s no native caption-file support on most servers) and your video is watchable in the sound-off timeline and describable to screen-reader users.
Every limit on this page is a default, and instance admins can change them. If video is part of your strategy, check your home server’s limits once — they’re usually listed on the about page or discoverable by simply trying an upload. Posting through the API (as schedulers like SocialKit do) honors the same server-side rules as the web composer.
1920 × 1080 px (16:9) exported as H.264 MP4 at a moderate bitrate is the dependable choice. Vertical and square also display fine — they render inside the post card rather than full-screen.
There’s no fixed time limit on default servers — the ~99 MB file cap is the real constraint. At 720p and a lean bitrate that’s roughly three minutes; at high-bitrate 1080p, closer to ninety seconds.
Mastodon is decentralized — each instance sets its own media limits, with 99 MB video and 16 MB images as the software defaults. Check your home server’s about page if you plan regular video posting.
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