WordPress: This File Cannot Be Processed by the Web Server

"This file cannot be processed by the web server" is a file type error, not a file size error. That is not our interpretation — it is what Automattic's own troubleshooting page says, in a sentence almost nobody quotes.

If you landed here after twenty minutes of compressing a video, stop: a smaller version of the same file will fail in exactly the same way.

What this error actually means

WordPress.com's support page Troubleshooting image and other file uploads has a section called "Upload error messages". It opens with a line worth reading carefully:

"WordPress shows one of these messages when an upload fails. Each message points to a different cause."

The entry for the message you are seeing reads, verbatim:

""This file cannot be processed by the web server." The file type is not supported. This message is not about the file's size. See use a valid file type."

Three things are packed into that:

1. The cause is the file type. The uploader rejected the format, not the byte count.
2. Size is explicitly ruled out. The page denies that cause outright, which official docs rarely bother to do.
3. Each message maps to one cause. The same page lists two other strings — "Unexpected response from the server." and "The server cannot process the image." — so if the wording you see is not the wording above, you are chasing a different problem.

One qualification that matters before you act on any of this: that page is WordPress.com's. Self-hosted WordPress produces its own strings for the same underlying situation. The block editor's audio documentation says: "If you try to upload a file type that is not supported, the editor will display an error message: Sorry, this file type is not supported here." On a Multisite network the string is different again: "Sorry, this file type is not permitted for security reasons". Same family of problem, three different sentences, and only the first one is documented as being unrelated to size.

Which file types WordPress.com actually accepts

The rule is a whitelist, stated plainly on the Accepted file types page:

"WordPress.com restricts uploads to the file types listed on this page. Restricting file types protects your site from unsafe files."

The troubleshooting page says the same thing from the other direction: "WordPress.com supports these common file types. Uploading any other file type causes an error."

The video section of that list is short:

.mp4, .m4v (MPEG-4)
.mpg
.mov (QuickTime)
.vtt (text captions for video)
.avi
.ogv (Ogg)
.wmv (Windows Media Video)
.3gp (3GPP)
.3g2 (3GPP2)

Audio is shorter still: .mp3, .m4a, .ogg, .wav, .flac.

Two entries people trip over:

• .webm is named as a format you cannot upload without help. The same page says that if you need a file extension not listed on it, "such as .mobile, .epub, or .webm, you can add support for these file types via a plugin—plugin-enabled sites run on more advanced infrastructure that can support file types not normally accepted." This is a genuine split between the two WordPresses: WordPress core's own MIME table maps webm to video/webm and mkv to video/x-matroska, so a self-hosted install and a WordPress.com site do not agree here.
• .mkv simply is not on the WordPress.com list, and unlike .webm it is not named anywhere on that page either. Treat it as "not listed", not as "banned" — the official docs do not say more than that.

The fastest fix: convert it before you upload

You do not have to reason this out yourself. The troubleshooting page gives the action directly:

"If you have images and other files in unsupported formats that you want to use, then you should convert them to a valid file type before uploading. You can do this with editing software or a free online converter."

MP4 is the target to aim at. It is on the WordPress.com accepted list, and it is in WordPress core's default MIME table as mp4|m4v. WordPress.com's own Recommended video settings page points the same way, but read its scope carefully: the "Convert a video" section says "a tool like HandBrake can be used to convert it before you upload it to the Media Library", and the instruction that follows — "Ensure "MP4" is selected in the "Format" dropdown, and "Web Optimized" is checked." — is a step inside HandBrake, not a WordPress setting.

That runs in your browser tab: the file is read from disk, re-encoded locally, and handed back. Nothing is uploaded to us — which matters when a failed upload is why you are here. If your rejected file is the .webm case above, use WebM to MP4 instead; the rest of the converters are in all Clapr tools.

One honest caveat: .mov is already on the accepted list, so converting QuickTime to MP4 is not what makes WordPress.com accept it. What it buys you is landing on the format that every WordPress list agrees on — useful when the file has to work in more than one place. WordPress.com's recommended specifications, which apply "for best results, and highest compatibility with other WordPress editor blocks (other than the Video or VideoPress block) such as the Cover or Story blocks", name h.264 as the format.

Other causes, in order of likelihood

1. You are on self-hosted WordPress, and the allowed list is not fixed. In core, get_allowed_mime_types() starts from the full MIME table and then removes entries. swf and exe come out unconditionally; htm|html and js come out only when the user lacks the unfiltered_html capability. That means the accepted set depends on who is logged in, which explains uploads that work for an administrator and fail for a contributor.

2. You are on a Multisite network. The network's Upload Settings screen carries its own "Upload file types" field, and its documentation warns that adding a type there is not enough on its own: "Adding mime types in the 'upload file types' field not listed in the default set will NOT work unless you've added them using the upload_mimes filter!" That path fails with the security-reasons wording, not the web-server wording.

3. The message you are actually seeing is one of the other two. If it says "Unexpected response from the server.", the documented advice is the opposite of urgent: "The upload often worked anyway. Reload your Media Library and check whether the file is there before you upload it again." If it says "The server cannot process the image.", the page describes the failure as "usually temporary rather than a problem with the image itself" and tells you to wait a few minutes and retry.

4. It really is about size — but then you get a different failure. On WordPress.com the documented guidance is that "You can reliably upload files up to 2 GB", and that beyond that "A larger file can fail partway through the upload." Note the wording: fail partway through, not refused up front. Your remaining plan storage is a second ceiling — "You cannot upload a file that is larger than the storage space remaining on your site."

5. Filename characters. Not a cause of this error, but on the same troubleshooting page: "Name your files using letters and numbers. WordPress replaces other characters with a hyphen (-), so naming files correctly before you upload them keeps their names predictable." Worth doing while you are re-exporting anyway.

How to tell it worked

Upload the converted file and watch which of the three messages appears — or none. If the web-server message is gone, the file type was the problem. If it comes back on a file whose extension is on the accepted list, you are no longer in the documented case and should check the official documentation for your specific setup. If a different message appears, start from the list above rather than converting again; per the official page, each message points to a different cause.

FAQ

Does "this file cannot be processed by the web server" mean my file is too large? No. WordPress.com's troubleshooting page states it directly: "The file type is not supported. This message is not about the file's size."

Which video files can I upload to WordPress.com? The Accepted file types page lists .mp4, .m4v, .mpg, .mov, .vtt, .avi, .ogv, .wmv, .3gp and .3g2. Anything outside the page's lists causes an error, per that same page.

Why does my WebM file fail when WordPress supports WebM? Because two different official lists disagree. Core's MIME table includes webm, but WordPress.com names .webm as an extension "not listed on this page" that requires a plugin. Which list applies depends on where your site is hosted.

Is this the same as "Sorry, this file type is not permitted for security reasons"? Related but not identical. That string is documented for Multisite networks, where the network's upload file types setting and the upload_mimes filter both come into play. The web-server wording is the one documented on WordPress.com's troubleshooting page.

Will converting to MP4 always fix it? It fixes the case where the format was outside the accepted list. It does not help if you are hitting storage limits, a Multisite restriction, or one of the other two error messages — see more upload fixes and the supported-formats walkthrough for Google Drive for how differently platforms handle the same files.

Quotations from WordPress.com's Troubleshooting image and other file uploads, Accepted file types and Recommended video settings pages, and from WordPress core's wp_get_mime_types() and get_allowed_mime_types() reference, checked 16 September 2026. Verify against the official documentation before relying on any of it.