Will this video publish?
Most video upload failures come down to three things: the file is bigger than the network's cap, it is longer than the network allows, or it uses a codec the network does not accept. H.264 in an MP4 container is accepted everywhere; HEVC (H.265), AV1, VP8 and VP9 are where it gets uneven — and several platforms accept codecs their own documentation says they do not. This page reads your file's real container, codec, resolution and duration in your own browser, without uploading anything, and tells you which networks will take it.
Two small slices are read in your browser to identify the codec. The file never leaves your device.
Video limits by network
These are the limits our own publisher enforces before it uploads. A dash means we track no cap for that network — not that it has none.
| Network | Max size | Max length | Codecs not documented |
|---|---|---|---|
| Bluesky | 100 MB | — | none |
| Mastodon | 99 MB | — | noneuntested |
| — | — | none | |
| — | — | VP8 | |
| Threads | — | 5m 00s | VP8 |
| X | 100 MB | — | HEVC (H.265), AV1, VP8, VP9untested |
| 500 MB | — | HEVC (H.265), AV1, VP8, VP9untested | |
| 2 GB | — | AV1, VP8, VP9untested | |
| YouTube | 2 GB | 3m 00s * | noneuntested |
* YouTube's three minutes is not a rejection: a longer video publishes as a normal video rather than a Short.
What we actually tested
We tested this rather than trusting the docs. In seven live publish tests in August 2026: AV1 published to Facebook, and Meta's Reels spec does list AV1 and VP9 as supported. AV1 and VP9 both published to Instagram and Threads, even though their docs say "HEVC or H264". AV1 and HEVC both published to Bluesky, which transcodes via video.bsky.app and accepts MP4, MPEG, WebM and MOV.
Each of those platforms had a codec list in our publish path before the test and an empty or shorter one after it. The pattern is that platforms transcode on ingest and accept far more than they document — but we do not act on the pattern alone, because the first entry disproven was disproven precisely by someone stopping to check rather than assuming.
The X, LinkedIn and Pinterest lists are marked untested above and mean exactly that: the docs say no and nobody has watched one fail. X's media spec sits behind a paywall, LinkedIn's Videos API states only "File format: MP4" without naming codecs, and Pinterest's is not publicly retrievable. Treat those three warnings as documentation, not evidence.
If a video fails on a network whose list says it should work, or publishes on one that warned, we want to know — tell us and the list gets corrected.
Common questions
- What video format works on every social network?
- H.264 video in an MP4 container, at 1080p or below. It is the one combination every network in this list documents as supported, and the safe answer whenever you only want to export once. Everything else — HEVC, AV1, VP8, VP9 — is accepted somewhere and warned about somewhere else.
- Does Bluesky support HEVC?
- Yes. We published an HEVC video to Bluesky and it went through, as did AV1. Bluesky transcodes uploads via video.bsky.app and accepts MP4, MPEG, WebM and MOV, so its codec list in our own publish path is empty — not because we assume it is permissive, but because we tested it.
- What is the video size limit for X, LinkedIn, Bluesky and Mastodon?
- X caps video at 100 MB and Bluesky at the same; Mastodon's default is 99 MB, though a server can change it. LinkedIn allows 500 MB, and Pinterest and YouTube 2 GB. These are the caps our publisher enforces before it uploads, so a file over one of them fails here rather than halfway through a transfer.
- Is my video uploaded anywhere?
- No. Two 512 KB slices are read from the file in your own browser to identify the container and codec, and a hidden video element reads the duration and resolution. Nothing is sent to us or to anyone else — a 2 GB file costs about a megabyte of reading and never leaves your device.
- Why does it say “may not publish” instead of “will fail”?
- Because documentation and behaviour disagree, and we would rather be accurate than confident. Several platforms accept codecs their own specs do not list: AV1 published fine to Facebook, Instagram and Threads despite their docs naming only H.264 and HEVC. A warning here means the network does not document that codec as supported — not that we watched it fail.
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