Loom's upload specification lists five containers: "Supported containers: MV, AVI, WEBM, MP4, MOV (Up to 4GB)". That exact line appears word for word on three different Loom help pages — the encoding settings article, the upload guide, and the upload-failure troubleshooting KB — and the first entry in it is worth looking at closely before you trust any third-party list.
The limits, at a glance
| What | Loom's wording | Page |
|---|---|---|
| Containers accepted on upload | "Supported containers: MV, AVI, WEBM, MP4, MOV (Up to 4GB)" | Loom video encoding settings |
| Size and length ceiling | "Loom limits uploads to 4 GB or 12 hours, whichever is less." | Upload or import videos |
| Mobile | "We do limit Mobile uploads to 4GB limit or 12 hours, whichever is less." | Upload or import videos |
| Files per batch | "you can upload up to 10 videos at a time" | Upload or import videos |
| Total number of uploads | "There is no limit to how many videos you can upload." | Upload or import videos |
| Who can upload | "Business, Business + AI or Enterprise plans" | Upload or import videos |
| Upload speed suggested | "at least 5 Mbps" | Upload-failure KB |
| Format you get back on download | "All videos downloaded from Loom will be in a .MP4 format." | Loom video encoding settings |
About that MV entry
The first container in Loom's list is MV. It is not a transcription slip on our end: the identical row appears on the encoding settings page, on the upload help page, and in the upload-troubleshooting KB article, all three reading MV, AVI, WEBM, MP4, MOV.
It is tempting to silently read that as MKV or M4V. Don't. None of the three pages that print this list defines what MV stands for, so any expansion of it is a guess rather than a spec. If you have a file whose extension you were hoping MV covers, the reliable route is the one Loom itself recommends further down this page: re-export to H.264/AAC in an MP4 container and upload that.
Before format: can you upload at all?
Uploading is gated by plan, not just by file type. Loom's upload page restricts the feature to "Business, Business + AI or Enterprise plans" and adds: "Uploads are not available for Business + AI Trials." The Business plan FAQ carries a matching note: "Please note the Upload feature is temporarily unavailable for Business Trial users."
So on a Starter (free) workspace, the supported-format question never comes up — there is no upload button to reject your file. Free-plan users run into a different ceiling instead, covered in Loom's 25-video storage limit.
"4 GB or 12 hours, whichever is less"
Read that phrasing carefully, because it is two separate ceilings and either one is enough to stop you. A tightly compressed 12-hour screen capture can sit well under 4 GB and still be refused on length. A 20-minute 4K export can be nowhere near 12 hours and still be refused on size. The same 4 GB / 12 hour pair applies to mobile uploads.
Why a supported format still fails
This is where most people get stuck: their file is an MP4, MP4 is on the list, and Loom still shows a failure. Loom names three causes:
"You may receive a Failed to process message after attempting to upload a video. This most often occurs because the file is over 4 GB, its frames per second are over 60, or its resolution is over 4096 x 2160."
Three numbers to check against your export settings: 4 GB, 60 fps, 4096 x 2160. A 120 fps gameplay capture and an 8K drone clip are both perfectly valid MP4 files and both fall outside those bounds.
Note Loom's own hedge — "most often occurs because" — so these three are the common causes, not a complete list. The troubleshooting KB names one more specifically: "There are times when an underlying property of your video is not supported (like the number of audio channels is too high) and this can only be fixed by running the media through Handbrake."
Audio channel count is a real rejection cause, and nothing in the file extension tells you about it. A 5.1 mix exported from an editor looks exactly like any other MP4 from the outside.
What to do with a rejected file
Loom's advice is unusually direct for a vendor, and it is the same on all three pages:
"The Loom uploader is designed to handle a broad range of video formats, containers, and codecs. If the file you want to upload to Loom is not supported, or even if the quality of the uploaded video doesn't turn out quite right, try running your video through Handbrake ."
"We recommend exporting your video using the media specifications in the above table (H.264/AAC to . MP4 file.)"
That is the target to hit: H.264 video, AAC audio, MP4 container. If your source is a QuickTime file off a Mac, an iPhone, or a screen recorder, the conversion is a single step and does not need a desktop install:
Try it right here
Runs in your browser. Your file is not uploaded anywhere.
This runs inside your browser tab — the file is read from disk, re-encoded locally, and handed back. Nothing is uploaded to a server, which is the point when the file you are fixing is already too big to upload comfortably. Same job, dedicated page: MOV to MP4. If the problem is the 4 GB ceiling rather than the container, compress the video first and upload the smaller result.
What Loom does to the file after it lands
The upload row in Loom's encoding table describes what your video becomes on Loom's side, not what you handed it:
- Video: "Codec: H.264, Frame Rate: Target 30fps, Bitrate: Variable bitrate."
- Audio: "Codec: AAC, 48kHz, Channels: 1 Channel (Mono), Variable bitrate."
- Resolution: "Up to 4K video (360p, 480p, 720p, 1080p, 1440p, 2160p)", with Loom encoding "all resolutions starting with the originally recorded resolution, down to 480p."
The mono line is the one to notice if you care about audio: Loom's uploaded-video spec lists 1 Channel (Mono). The table states the channel count without explaining it or offering a setting, so take it as written.
On bitrate, the table says only "Variable bitrate" — no kbps figure, for video or audio. On the way back out, downloads are always .MP4, and Loom describes those specs as "similar to the RAW media recorded" — similar, not identical.
Platform-specific gotchas
- Ten at a time. "you can upload up to 10 videos at a time", though there is no cap on how many you upload overall.
- Closing the modal does not cancel. "Your videos will keep uploading even if you leave the upload modal. The uploads only stop if you select cancel."
- Big files sit in processing. Loom warns that "Videos that are large in resolution, size, or duration will take longer to process and may remain in a processing state after uploading." A stuck-looking upload is often just a large one.
- Connection floor. The troubleshooting KB suggests "a strong and stable internet connection with an upload speed of at least 5 Mbps."
FAQ
What video formats does Loom support for upload?
Loom's official table reads: "Supported containers: MV, AVI, WEBM, MP4, MOV (Up to 4GB)". That is the full published list, quoted as Loom writes it, including the MV entry.
What is the maximum file size I can upload to Loom? "Loom limits uploads to 4 GB or 12 hours, whichever is less." Both ceilings apply independently, and the same pair applies to mobile uploads.
Why does my MP4 fail to upload even though MP4 is supported? Loom says a "Failed to process" message "most often occurs because the file is over 4 GB, its frames per second are over 60, or its resolution is over 4096 x 2160." Loom also names too many audio channels as a cause that only re-encoding fixes.
Can I upload videos to Loom on the free plan? No — Loom restricts uploading to "Business, Business + AI or Enterprise plans", and notes that "Uploads are not available for Business + AI Trials."
Does MV mean MKV?
The list is printed identically on three Loom pages and none of them defines the entry, so treat any expansion as unconfirmed and check the official documentation. If you need that file in Loom, convert it to H.264/AAC MP4 — what Loom recommends for anything its uploader refuses.
What format do I get when I download a Loom video? MP4, always: "All videos downloaded from Loom will be in a .MP4 format." The encoding is described as "similar to" the original recording.
More platform ceilings like this one are collected in the limits section, and every converter mentioned above is listed on the Clapr tools page — all of them run locally in your browser.
Quoted from Loom's help center, checked 16 September 2026. Loom's own pages disagree with each other in places; verify against the official documentation before relying on a number.
