Choose a local conversion or editing tool
Check support before processing a large file.
Prepare
Choose the task first: convert a format, trim a time range, compress a file, or generate captions. A filename extension does not guarantee that the browser can decode the file’s codec. Read the compatibility information shown by the tool.
Work through the decision
Test a short representative file before a large batch. Preserve the original and compare transparency, audio tracks, text, or animation as appropriate. A smaller output is useful only if it retains the content you need.
Review the result
When a tool processes locally, keep the tab open until the download is ready and use its cancel control to stop work. Browser memory limits and available codecs vary, so treat an unsupported notice as a real limitation rather than renaming the extension.