platform limit
mastodon video size limit.
Mastodon accepts video uploads up to 99 MB. Convert your clip to WebM with Basketweaver and it lands under 4 MB, comfortably inside that limit.
The maths
A file budget divided by duration gives you a bitrate. For a 30 second clip targeting 4 MB with 96 kbps of audio:
(4,194,304 bytes x 8) / 30s / 1000 = 1118 kbps total 1118 - 96 kbps audio = 1022 kbps of video
Basketweaver runs this for you and steps the resolution down when the numbers cannot be met at a watchable quality.
Three ways to do it
Open the converter with the Mastodon target already set, or convert on your phone:
Mastodon specifics
This is the default compiled into Mastodon itself (VIDEO_LIMIT = 99.megabytes). Instance admins can raise or lower it and many run well below the default to control storage, so treat it as a ceiling rather than a promise and check your own instance.
Long clips
A three or four minute clip fits under 4 MB the same way people do it by hand with ffmpeg: the resolution comes down as the clip gets longer. Five minutes is the maximum.
| Clip length | Resolution | Video bitrate |
|---|---|---|
| 30 seconds | 720p | 1038 kbps |
| 1 min | 480p | 519 kbps |
| 2 min | 360p | 260 kbps |
| 3 min | 240p | 173 kbps |
| 4 min | 240p | 130 kbps |
| 5 min | 240p | 104 kbps |
Audio is removed. At three minutes a 96 kbps track would take over half the budget, so all of it goes to the picture.
Questions
- What is the largest video I can upload to Mastodon?
- Mastodon accepts uploads up to 99 MB. That figure was read on 2026-09-01 from Mastodon's own documentation.
- How do I get a video under 99 MB?
- Convert it to WebM with Basketweaver. Output is capped at 4 MB, which is inside Mastodon's 99 MB ceiling, so a converted clip always fits. Conversion runs on your own device or in your own browser.
- What bitrate do I need for a 30 second clip?
- Budget 1022 kbps of video alongside 96 kbps of audio. That is the target size in bits divided by the duration, minus the audio track. Basketweaver works this out for you and lowers the resolution when the maths cannot be met.
- How long can the video be?
- Up to five minutes. Longer clips are not rejected for being large, they are encoded at a lower resolution: roughly 720p at 30 seconds, 240p at three minutes, and 240p at five. That trade is what lets a three or four minute clip land under 4 MB at all, and it is the same trade people make by hand with ffmpeg.
- Does the converted file keep its audio?
- No. Audio is removed. At these sizes a 96 kbps audio track would consume over half the budget of a three minute clip, so the whole budget goes to the picture instead.
- Is this limit still current?
- It was checked on 2026-09-01 against Mastodon's own documentation. Platforms change these quietly, so the source is linked on this page for you to confirm.