Question 1

How does video compression work here?

Accepted Answer

The tab re-encodes with FFmpeg using H.264. You pick a quality preset. The file is not uploaded.

Question 2

What do High, Balanced, and Maximum mean?

Accepted Answer

High is CRF 23. Balanced is CRF 28. Maximum makes the smallest file and may drop resolution.

Question 3

What formats can I drop?

Accepted Answer

MP4, WebM, MOV, AVI, MKV, and most common clips. Output is always MP4 H.264.

Question 4

Is there a size limit?

Accepted Answer

Yes. Stay under 500MB. Larger files belong in desktop software.

Question 5

Why is the first run slow?

Accepted Answer

The engine is about 25MB and downloads once. Later visits use the browser cache.

Question 6

Does the video leave my device?

Accepted Answer

No. Encode runs in the browser.

Question 7

Will I lose audio?

Accepted Answer

Audio is kept in the usual case. If a rare codec fails, try Convert Video or a desktop encoder.

Question 8

Can I compress 4K?

Accepted Answer

Sometimes, if the file is under 500MB and the machine has RAM. If the tab dies, use HandBrake.

Question 9

Is this the same as Compress Image?

Accepted Answer

No. This page is for video. Photos go to Compress Image.

Question 10

Can I pick a custom bitrate?

Accepted Answer

No. You pick a preset. That is enough for email and chat.

Question 11

What if I need a GIF?

Accepted Answer

Use Convert Video. This page outputs MP4.

Compress Video - Shrink MP4 in the Browser