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Each provider has its own media rules. One destination accepts a video, and another destination refuses the same video. OpenPMM compares your media with the rules of every selected destination before it publishes the post. Use this page for the general rules. Use the destination pages for the exact limits.

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What you can upload

The 500 MiB limit is an OpenPMM limit. Some providers accept a larger file, but OpenPMM does not. Send the exact content_type and byte_size of the file when you create the upload. For the three upload steps, see Upload assets. video identifies the uploaded file type. It does not select a provider placement. For YouTube, set destination_options.youtube.kind to video or short. Provider pages describe the equivalent placement options for other Destinations.

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Publication checks

Upload the file, attach it to the Post, and publish normally. OpenPMM returns no separate compatibility result when the file can publish. If a selected Destination needs a different file, OpenPMM returns status 422 with code media_change_required. No provider request has started. Each entry in errors identifies the Asset, Destination, property, actual value, required value, and allowed actions. A readable file stays in the Workspace library even when it cannot publish to one Destination. You can use it for a different Destination. See Resolve media changes for the error shape and recovery workflow.
A provider can still refuse media for rights, moderation, or account rules. Read the Post after publication to get the provider result.

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Destination guidelines

X

Up to four assets. Short video with strict dimensions.

LinkedIn

One video, or up to 20 images. MP4 video only.

Bluesky

Publish text with up to four sanitized images.

Facebook

One video for a Reel. Images for a feed post.

Instagram

One video for a Reel or a Story. Up to 10 images for a post.

Threads

Up to 20 assets. MP4 fast start for video.

TikTok

Exactly one video. Your creator account adds a duration limit.

YouTube

Exactly one video. Shorts have their own limits.

Mastodon

Your instance reports the media limits.