Why video uploads fail
An upload that stops, stalls, restarts or is rejected is almost always one of a short list of causes. Learn to tell them apart from what the browser shows you, and fix the right one.
Video uploads fail for one of five reasons. The connection dropped. The computer or tab stopped. Something on the network refused a large or long request. The file is too big or not an accepted video. Or the file was already broken before upload. Each shows up differently, and each has its own fix.
The error message, when there is one, is rarely the cause. Think of a progress bar that stalls at 63 percent, a page that reports a network error, or an upload that completes but gives a video that ends early. Each points to a different failure. Treating them the same wastes hours. The good news is that the list of causes is short. The symptoms are easy to tell apart once you know what to look for.
This guide is organised by symptom. Find the one that matches what you saw, read the likely causes, and apply the fix. It assumes a resumable uploader such as VideoBB's, which changes the picture a lot. With one, a dropped connection is a pause, not a failure. Where a plain form upload behaves differently, that is noted. The uploading video hub covers the steps that come before a failure, such as preparing the file.
Symptom to cause
Start here and jump to the matching section below.
| What you saw | Most likely cause | Section |
|---|---|---|
| Progress stalls, then continues | Brief network interruption; the uploader resumed | Network drops |
| Progress stalls and never continues | Connection lost and not restored, or computer slept | Sleep, tabs and power |
| Fails at the same percentage every time | A proxy, VPN or firewall limit; or a corrupt region of the file | Network path limits |
| Rejected immediately | File over the size limit or not an accepted container | The file itself |
| Upload completes; video ends early or will not process | Truncated or damaged source | The file itself |
| Very slow but steady | Low upstream bandwidth or competing traffic | Speed, not failure |
Network drops
The commonest cause, and with a resumable uploader the least serious. Wi-Fi roams between access points. Mobile connections hand over between cells. Home routers renew leases. Each of these can drop a TCP connection for a moment. A single-request upload dies at that instant and starts again from zero. A tus uploader notices the failed chunk, waits, asks the server for its offset and continues. From the user's side the progress bar pauses and then moves again. If this happens often, the fix is a better connection, not anything in the browser. Move closer to the access point, or plug in an Ethernet cable. Resumable uploads explained shows why the recovery is so cheap.
Sleep, tabs and power
An upload runs inside a browser tab, and the tab has to be alive. Closing it ends the upload. On VideoBB the progress is kept on the server for 48 hours. Reopen the upload page in the same browser, select the same file, and it resumes. But nothing happens while the tab is closed. Putting the computer to sleep drops the network entirely. Some browsers throttle background tabs aggressively, and some operating systems suspend network activity for applications in the background on battery. The fix is mundane: plug in the power, disable sleep for the duration, and keep the tab in the foreground. The 2 GB upload guide lists the full set-up.
Network path limits
Between the browser and the server sit routers, possibly a corporate proxy, possibly a VPN, and the host's own load balancers. Each may set a maximum request size or a maximum time a request may stay open. Some add an inspection step that dislikes large binary uploads. A plain form upload hits these as a 413 Content Too Large, a 408 or 504 timeout, or a silent reset partway through. It will fail at roughly the same point every time. Chunked uploads mostly avoid this, because every request is small. But a proxy that limits total connection time or blocks PATCH requests can still interfere. The diagnostic is to try the same file on a different network: a phone hotspot is the quickest test. If it succeeds there, the problem is on the office or home path. The usual fixes are to disconnect the VPN, or to ask whoever runs the proxy to allow the upload host.
The file itself
Many failures have nothing to do with the network. VideoBB accepts files up to 4 GB in mp4, mkv, avi, mov, webm, m4v, mpg, wmv, flv, ts and 3gp. The help page on supported formats and size limits keeps the current list. A file over the limit is refused when the upload is created, since the uploader declares the size before sending a byte. Some files are not really video: a project file, an image sequence, a zipped folder or a document with a video extension. These upload fine and are then rejected when the server probes them. A truncated file, from a cancelled export or an interrupted copy, also uploads fine. Then it either fails to process or gives a video that ends early. The fix in every case is on your side. Check the size in the file manager. Play the file locally and scrub to the end. If in doubt, run ffprobe from the FFmpeg toolkit to confirm the container, codecs and duration. If the container is the problem, the free video converter turns the file into a standard MP4. Container vs codec explains what ffprobe is telling you, and prepare video for upload shows how to export a file that passes first time.
Files that are commonly mistaken for uploadable video
- Editor project files (.prproj, .fcpbundle, .drp, .kdenlive): these describe an edit and contain no video.
- Image sequences or a folder of frames, even when zipped.
- Screen recordings that were still being written when copied, which are truncated.
- Files renamed from one extension to another without conversion; the container inside is unchanged.
- DRM-protected downloads, which will not decode outside the application that made them.
Speed, not failure
Sometimes nothing has failed. The upload is simply slow. Upstream bandwidth on most connections is a fraction of downstream, and a backup client or another device may be using part of it. A 2 GB file on a 5 Mbps upstream takes about 53 minutes with the connection to itself, and longer when shared. The progress bar moving steadily, however slowly, is a healthy upload. Video upload speed and time has the table and the ways to shorten the wait. The short version: wire in and pause everything else.
A diagnostic sequence
Work through in order; most problems are identified by step three.
- Check the file: size under 4 GB, an accepted container, plays locally to the end.
- Check the environment: power connected, sleep disabled, tab in the foreground, other uploads paused.
- Retry once. A resumable uploader will continue from where it stopped; a one-off drop needs no further action.
- If it fails again at the same point, switch networks (hotspot) and retry. Success there means a path limit on the original network.
- If it fails on every network, try a different, known-good file. Success there means the original file is damaged.
- If a known-good file fails on every network, report it through the help centre with the file size, container, browser and the percentage at which it stops.
After a successful upload
A completed upload is followed by processing, and a few things that look like upload failures are actually processing states. A video that plays only at low quality for a while is waiting for its higher renditions. A video with a missing thumbnail for the first minute is waiting for asset generation. Both resolve on their own. What does not resolve is a source that was already poor. Heavy compression before upload survives transcoding. Why video looks blurry after upload explains why the fix is a better export, not a re-upload of the same file.
Frequently asked questions
My upload says 100 percent but the video is not available. Did it fail?
Probably not. After the last byte arrives the server verifies the file and starts transcoding, and the video becomes available as renditions are produced. Lower qualities appear first. If nothing appears after a reasonable wait, the source may have failed probing, which usually means it was not a valid or complete video file.
Why does my upload work on my phone but not at the office?
Because the office network has something on the path that the mobile network does not. It may be a proxy with a size or time limit, or a firewall that inspects or blocks certain requests. It may be a VPN that routes traffic through a narrow gateway. Disconnecting the VPN is the first thing to try. Otherwise, ask the network administrator to allow the upload host.
The file plays fine on my computer but is rejected. Why?
Playing locally proves the file is decodable by your player, not that it is in a container the host accepts or that it is complete. Check the actual container with ffprobe or your player's info panel. A file with an mp4 extension can be something else inside. Also confirm the duration matches what you expect, since a truncated file may still play.
Does using a VPN break uploads?
Not always, but VPNs add latency, can reduce bandwidth, and sometimes route through gateways with their own request limits. A resumable upload tolerates the latency but a hard gateway limit can still stop it. If an upload behaves badly on a VPN and well without it, that is the answer.
Sources
- MDN: 413 Content Too Large — The response from proxies and servers that cap request size.
- MDN: 408 Request Timeout — Timeouts that end long-running single requests.
- tus resumable upload protocol — How chunked uploads recover from interruptions.
- FFmpeg documentation — ffprobe for inspecting a suspect file.
Related guides
How to upload 2 GB video files
Large uploads fail for boring reasons: a sleeping laptop, a flaky Wi-Fi hop, a file that was never going to be accepted. Here is how to get a big file up in one go, and what to do when it stops.
Resumable uploads explained
A resumable upload is a conversation, not a single request. The client sends pieces and the server keeps count. After a break, they agree on where to continue. This is how the tus protocol does it.
Prepare video for upload
The right export is smaller, uploads faster, is accepted without complaint and transcodes cleanly. It is not the highest possible quality and it is not the smallest file. Here is the middle.
Container vs codec
A file extension names the wrapper. The codec is the compression inside it. Confusing the two is the root of most playback failures, and telling them apart takes one command.