Resumable upload
A resumable upload is a file upload that can pause or fail partway and then continue from where it stopped, rather than starting again from zero. The file is sent in pieces and the server remembers which pieces have arrived. This matters most for large video files and for users on unstable mobile networks.
Why it matters
Large videos on mobile networks fail often, and every restart from zero wastes the user's time and data. Lost uploads mean lost content, unhappy creators and support tickets. Resumable uploads turn a fragile process into one that survives tunnels, network switches and closed laptops, which directly affects how much content a platform receives. That behavior comes ready-made in FastPix's resumable upload SDKs for Web, iOS, Android and Flutter, so no one writes chunk tracking for each platform.
How it works
- The client tells the server it wants to upload a file and receives an upload ID.
- The file is sent in pieces, and the server records how much has arrived.
- If the connection drops, the client asks the server for the last confirmed position.
- The client sends only the remaining pieces, and the server joins them into one file.
How do resumable uploads work?
Resumable uploads work by sending a file in pieces and letting the server remember which pieces have arrived. Each upload has an ID. If the connection breaks, the client asks the server how far it got, then continues from that point. The server joins the pieces once the whole file is received.
Resumable upload vs multipart upload: what is the difference?
Resumable uploads focus on continuing after a failure, while multipart uploads focus on splitting a file into parts that can be sent separately, often in parallel. In practice they overlap. Many multipart uploads can be resumed, and many resumable protocols send data in parts. The key question is whether the client can find out what already arrived and skip it.
Where it's used
Creator apps and online learning platforms use resumable uploads so a long upload picks up where it stopped after a dropped connection, instead of starting again.
Where it usually goes wrong, and how FastPix handles it
Teams often add resumable logic late, after users complain about lost uploads, and then must handle chunk tracking and retries on every platform they support.
FastPix's upload SDKs for web and mobile split large files into chunks and resume after a dropped connection, so the app does not track chunks itself. Your team ships one upload flow across platforms instead of maintaining retry logic in each app.
