Drop in a video that Messenger, WhatsApp, Telegram, Instagram or X keeps rejecting. Video Fixer finds what's wrong and rebuilds it into a universal MP4 — entirely in your browser. Your file never leaves your device.
Drop your video here
The one that won't upload or play. We'll diagnose and fix it.
MP4 · MOV · MKV · WebM · AVI · Nothing is uploaded — it's fixed right here on your device.
Loading the video engine — one-time download, then cached…
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Everything runs on your device — your video is not being uploaded.
Most "video won't upload" and "unsupported format" errors have nothing to do with your video looking broken — the picture and sound are fine. The problem is how the file is packaged and which codecs are inside. Chat apps and social networks only accept a narrow, safe combination, and screen recorders, phone cameras and downloaders often produce something just outside it.
The single most common culprit is Opus audio inside an MP4 file. Opus is an excellent, modern audio codec, but the MP4 (.mp4) container is expected to carry AAC audio. Many Android screen recorders and download tools wrap Opus audio in an MP4 anyway. The file plays perfectly on your PC, but Facebook Messenger, WhatsApp, iPhones and many upload forms silently reject it or drop the sound. Swapping only the audio track to AAC fixes it — the video is never touched.
Other common reasons a video is rejected: it uses a newer video codec the target app can't decode (HEVC/H.265 from iPhones, AV1 or VP9 from web downloads); it's in a container that isn't accepted (MKV or WebM instead of MP4); its metadata is in the wrong place (a non-faststart MP4 won't start streaming and some uploaders reject it); or it has odd pixel dimensions or a non-standard pixel format (like 10-bit/HDR) that a strict encoder refuses. Video Fixer detects which of these applies and fixes only that.
| Problem in your file | Why it fails | What Video Fixer does |
|---|---|---|
| Opus audio in an MP4 (the #1 cause) | MP4 is expected to hold AAC; Opus-in-MP4 is rejected or plays with no sound | Re-encodes only the audio to AAC, copies the video untouched |
| HEVC / H.265 video (iPhone default) | Many apps and older devices can't decode it | Transcodes video to H.264 |
| AV1 video | New, efficient codec; little support on older devices/apps | Transcodes video to H.264 |
| VP9 video (often inside WebM) | Not accepted by MP4-only upload flows | Transcodes video to H.264 |
| MKV or WebM container | Many uploaders accept only MP4/MOV | Repackages into MP4 (stream-copy if the inner codecs are fine) |
| No faststart (moov atom at the end) | Won't start streaming; some uploaders reject it | Moves the moov atom to the front (+faststart) |
| Odd width/height | H.264 4:2:0 requires even dimensions — the encode aborts | Pads/scales to even dimensions |
| 10-bit / HDR / unusual pixel format | Many players expect 8-bit 4:2:0 | Converts to yuv420p 8-bit |
Output: always a single .mp4 — H.264 video (yuv420p) + AAC audio + faststart.
Drag in (or tap to choose) the video that won't upload. It loads straight into the page — no upload, no progress bar to a server.
Video Fixer inspects the container, video codec, audio codec, faststart flag and dimensions right on your device, and tells you in plain language what's wrong.
One click rebuilds the file into a universal MP4 (H.264 + AAC + faststart), re-encoding only what's broken and copying the rest untouched. Save it and upload it anywhere.
Reads: MP4, MOV, MKV, WebM and AVI containers, with video in H.264, HEVC/H.265, AV1, VP9 or MPEG-4 and audio in AAC, Opus, MP3, Vorbis, AC-3 and more.
Writes: a single .mp4 with H.264 video (8-bit yuv420p, even dimensions, faststart), and AAC-LC audio — the exact combination Messenger, WhatsApp, Telegram, Instagram, X, iPhone, Android and virtually every upload form accept.
Minimum work, maximum quality: any stream that is already compatible is copied, not re-encoded — so when only the audio, container or faststart is wrong, your picture is preserved bit-for-bit and the fix is near-instant.
No. Video Fixer runs entirely in your browser using WebAssembly. Your video is read, diagnosed and rebuilt on your own device — it is never sent to our servers or anywhere else. Nothing leaves your computer or phone.
Yes. After the page has loaded once, the whole engine is cached in your browser, so you can fix videos even with no internet connection. Because nothing is uploaded, no connection is needed to do the work.
It is the most common reason a video won't upload. Some screen recorders and download tools save Opus audio inside an MP4 file, but MP4 is expected to contain AAC audio. The video plays fine on your PC, yet apps like Messenger and WhatsApp reject it or lose the sound. Video Fixer converts just the audio to AAC and leaves the picture untouched.
As little as possible. Video Fixer does the minimum work: if a stream is already compatible it is copied bit-for-bit with no re-encoding and no quality loss. For example, when only the audio or the container is the problem, the video is kept exactly as it is. Quality only changes for parts that genuinely have to be re-encoded, such as HEVC or AV1 video.
Because everything runs in your browser's memory, the practical limit depends on your device's available RAM rather than an upload cap. Short and medium clips of a few hundred megabytes are comfortable on most computers and phones; very large files use more memory, so a desktop handles them best.
Any place that rejects your video or won't play it — Facebook Messenger, WhatsApp, Telegram, Instagram, X (Twitter), Signal, Discord, TikTok, email attachments and website upload forms. The universal MP4 it produces (H.264 + AAC + faststart) is accepted virtually everywhere, including iPhone and Android.
Yes, it is completely free, and no account, email or sign-up is required. There are no watermarks and no limit on how many videos you fix.
It reads common containers such as MP4, MOV, MKV, WebM and AVI, with video in H.264, HEVC/H.265, AV1 or VP9 and audio in AAC, Opus, MP3 and more. It always outputs a single MP4 with H.264 video, AAC audio and faststart enabled — the combination almost every app and device accepts.