Client-side media preflight can improve an upload experience, but it can also crash the page before the network request begins. A twelve-megapixel JPEG may be only four megabytes on disk and tens of megabytes after decoding. Creating several full-size canvases at once is enough to exhaust memory on older phones.
Preflight is policy, not editing
Decide what the browser must prove before transfer. Useful checks include file count, compressed byte size, declared type, readable dimensions, and a conservative duration limit for video. Avoid mandatory re-encoding unless the product truly needs it. Every transformation adds CPU time, memory pressure, battery use, and another failure mode.
Process one file at a time
A file picker may return twenty items. Do not decode all of them to build previews. Maintain a queue with one active decode on constrained devices and at most two on stronger ones.
