Which format is best for compressing small video files: WebM or MP4?

It's worth testing a small script that compresses your video with several settings for each format. Start with the tiniest output and check quality, then adjust settings as needed. I've managed to cut down video sizes significantly for different sources this way!

For the best outcome, try both formats and see which one gives you a smaller file size with acceptable quality. You might start off optimizing for MP4 using a high-compression codec like H.265/HEVC while adjusting the resolution and bitrate as low as you can.

WebM and MP4 are just container formats, so the file size mainly depends on the bit rate and the encoding method you choose, like AV1, H.264, or H.265. Advanced encoders like AV1 and H.265 can keep higher quality at lower bit rates, which can help you save space.

The choice between them isn't straightforward. Both can give you varying results based on the settings and content. It can depend on the video length and the resolution you aim for. So it's useful to experiment with both.

Honestly, just go ahead and create both formats and compare the results. It could be the simplest way to find out which one works better for your needs.