Multipart upload
A multipart upload is a method of sending a large file by splitting it into smaller parts that are uploaded separately and then joined back together on the server. Parts can be sent in parallel to speed things up, and a failed part can be retried alone. Cloud object storage services widely support multipart uploads for large media files.
Why it matters
Sending a large video as one piece is slow and fragile: one network error ruins the whole transfer. Multipart uploads finish faster by sending parts in parallel, and failed parts can be retried alone. For businesses moving big studio files or long recordings, this cuts transfer time and wasted bandwidth.
How it works
- The client starts a multipart upload and receives an upload ID from the storage service.
- It splits the file into parts and uploads them, often several at the same time.
- Each part is confirmed separately, and failed parts are sent again on their own.
- The client sends a final request, and the service joins the parts into one file.
What is the minimum part size for S3 multipart upload?
The minimum part size for Amazon S3 multipart upload is 5 MiB, except for the last part, which can be smaller. The maximum part size is 5 GiB, and one upload can have up to 10,000 parts. Amazon suggests considering multipart upload once a file reaches about 100 MB.
When should I use multipart upload for video?
Use multipart upload when video files are large, roughly 100 MB or more, or when users are on networks that drop often. Splitting the file lets parts upload in parallel, which speeds things up on fast connections. It also means a failure only costs one part, not the whole file.
Where it's used
OTT services and video platforms send very large video files in parts, often several at once, so uploads finish faster and failed parts can be retried.
By the numbers
- Amazon S3 multipart uploads allow up to 10,000 parts, with each part between 5 MiB and 5 GiB, and the last part having no minimum size. (Amazon S3 multipart upload limits)
