Why compress it myself if WhatsApp already does?

Because you choose the quality and resolution, it sends faster, and the video takes up less space on the recipient’s phone.

Is there a length limit?

In the browser, yes, to protect your computer: usually up to 5–10 minutes and 200–500 MB, depending on memory. The desktop app has no limits.

Shrink a video before sending it on WhatsApp: you choose the quality, it sends faster, and it is never uploaded to any server.

1Drop the video into FeatherFiles (MP4, MOV or WebM).
2Choose «Light video for sharing» (480p, about 7.5 MB per minute) or «Videos» (720p, about 14.5 MB per minute) for higher quality.
3Download the result and send it on WhatsApp. No watermarks, no sign-up.

Why compress it myself if WhatsApp already does?: Because you choose the quality and resolution, it sends faster, and the video takes up less space on the recipient’s phone.
Is there a length limit?: In the browser, yes, to protect your computer: usually up to 5–10 minutes and 200–500 MB, depending on memory. The desktop app has no limits.