Browser Video Trimming Compatibility: MP4, MOV, M4V, and WebM

MP4, MOV, M4V, WebM, and MKV are containers that can hold different video and audio encodings. Two files with the same extension can behave differently if their internal tracks use different codecs, profiles, bit depths, or audio formats. The browser must be able to read the source before Save Replay can preview and prepare the selected range.

The accepted-file list is therefore deliberately conditional: MP4, MOV, M4V, and WebM files that the browser can decode and prepare. Save Replay does not promise that every possible media combination inside those containers will work on every browser and operating system.

Changing a filename from recording.mkv to recording.mp4 does not rewrite the container or its internal structure. Software still reads the original bytes, so the renamed file remains an MKV with a misleading extension. Use a real remux operation when the tracks can be placed into a different container without re-encoding.

OBS includes File → Remux Recordings and documents automatic remuxing options. Its recording guide recommends MKV for resilience and provides remuxing to MP4 for editing and sharing compatibility. This preserves the reliable capture workflow while producing a source Save Replay can attempt to decode in the browser.

Save Replay's product promise is that only the selected clip should be uploaded. If the browser cannot prepare the selected range safely, falling back to the complete source without clear consent would violate that promise and could transfer far more data than the user intended.

The current flow stops and explains the limitation instead. Try a current desktop browser, verify the source plays locally, remux a compatible capture when appropriate, or convert the file with a trusted tool. Keep the original until the prepared clip has been reviewed and the watch page is ready.