MP4 to WebM: a web-delivery copy needs a playback check
WebM can suit a web page or a system that accepts it, but conversion is not merely putting an unchanged clip in a new box. Re-encoded video is a delivery copy to check, not a replacement for the filming original.
Start with the destination’s requirements
WebM is a media format designed for the web and can carry video and audio with suitable encodings. Playing on your device is not enough if the destination does not support the resulting file.
Check the requested format first and try the clip in its actual player. Keep the original MP4; do not create WebM only because its name sounds newer.
References: WebM Project — Format and playback questions
Know the delivery copy’s limits
The current path may scale the image down to fit 1280 × 720 pixels while preserving aspect ratio and produces 30 frames per second. It is not a promise to retain the source resolution or frame cadence unchanged.
Inspect onscreen writing and fast motion after conversion. Settings suitable for an ordinary clip may not preserve a detailed screen recording, even when the file plays without an error.
File size alone cannot settle acceptance
Check the beginning, middle and ending, including sound matched to a visible action. If the source is silent, conversion does not add sound.
Measure the downloaded file rather than assuming a fixed saving. Use the delivery copy when it serves its purpose, and return to the source for future editing instead of repeatedly recycling compressed exports.
Example: reducing a widescreen clip
A 1920 × 1080 video reduced by a factor of 2/3 becomes 1280 × 720. Pixels per frame fall from 2073600 to 921600, about 44.44% of the original count. That is not the predicted percentage of final file bytes.
If the video shows a small-font table, play the output at its normal display size and read the numbers. A successful conversion or smaller file is insufficient if the essential information becomes illegible.