Compress Video for Slack
Shrink clips to a courteous ~10 MB so they upload in seconds and play inline on the first click for the whole channel. Slack streams your exact upload and never re-compresses it — so a smaller file is simply faster for everyone. Private, free, and runs 100% in your browser.
Target size
Bitrate-calculated to fit
Privacy-first
Videos never leave your device
Fast processing
WebCodecs + mediabunny
We calculate a target bitrate from your video's duration so the output fits under 10 MB (Slack). Longer clips get less bitrate per second, so trimming first gives the best visual quality.
Target Size: Under 10 MB (Slack)
We calculate a per-video bitrate from duration, then re-encode with H.264 + AAC. If the first encode overshoots, we retry at 10% lower bitrate (up to two retries).
Drop files here
or click to browse
About Compress Video for Slack
Slack accepts files up to 1 GB each, even on the free plan, so almost any video technically uploads. The catch comes afterward: Slack stores and streams your exact upload and never re-compresses it, so a 200 MB screen recording is served to every teammate at full size — it crawls up your connection and then buffers in the inline player for everyone who opens the channel. Post something large in a busy thread and people sit on a spinning preview. This tool shrinks any MP4/MOV/WebM clip to a courteous ~10 MB that uploads in seconds and plays on the first click for the whole team.
We read the video's duration and calculate a target bitrate that fills 10 MB without overshooting. For a one-minute clip that lands around 1.3 Mbps — plenty for crisp 720p and perfectly watchable 1080p — and it scales down linearly for longer videos. The output is MP4 with H.264 video and AAC audio, the exact combination Slack plays inline in its desktop, web, and mobile apps, so your clip previews on the first click with no download step.
Everything runs on-device in a Web Worker using WebCodecs and the mediabunny library. Your video is never uploaded, queued, or stored on a server — which matters when the clip is an internal demo, a customer call recording, or an unreleased product walkthrough you would rather not hand to a third-party converter. Close the tab and the file is gone.
Related Tools
Compress Video for Slack — Frequently Asked Questions
What is Slack's file upload size limit?
1 GB per file on the free plan; paid plans allow larger uploads. So most videos fit under the limit. The real catch is that Slack streams your exact upload without re-compressing it, so a large clip uploads slowly for you and buffers in the inline player for every teammate who opens it. On the free plan, files also drop out of history after 90 days. Compressing to around 10 MB keeps uploads quick and previews instant.
Why does my Slack video take so long to preview or upload?
Because Slack serves the original file as-is. Unlike WhatsApp or Instagram, it does not shrink your video on its end — it stores and streams the exact bytes you sent — so a large recording uploads slowly for you and buffers in the inline player for everyone who opens the channel. Pre-compressing to ~10 MB fixes both: it uploads in seconds and previews on the first click.
Does Slack compress videos automatically?
No. Slack stores and streams whatever you upload at its original bitrate and only generates a thumbnail preview. That is the opposite of chat apps that re-encode on send, and it is exactly why compressing before you post matters: what you upload is what your whole team streams.
Will a 10 MB video look good enough for work?
For most clips, yes. 10 MB comfortably holds 60–120 seconds of clear 720p, and screen recordings — mostly static frames that H.264 compresses very efficiently — often fit several minutes at 1080p with no visible loss. For long, high-motion footage, trim it first or accept softer results.
What formats can I upload, and what do I get back?
You can drop in MP4, MOV, WebM, or MKV. The output is always MP4 with H.264 video and AAC audio — the most compatible combination and the one Slack plays inline on web, desktop, and mobile without asking anyone to download it first.
What is Slack's file upload size limit?
1 GB per file on the free plan; paid plans allow larger uploads. So most videos fit under the limit. The real catch is that Slack streams your exact upload without re-compressing it, so a large clip uploads slowly for you and buffers in the inline player for every teammate who opens it. On the free plan, files also drop out of history after 90 days. Compressing to around 10 MB keeps uploads quick and previews instant.
Why does my Slack video take so long to preview or upload?
Because Slack serves the original file as-is. Unlike WhatsApp or Instagram, it does not shrink your video on its end — it stores and streams the exact bytes you sent — so a large recording uploads slowly for you and buffers in the inline player for everyone who opens the channel. Pre-compressing to ~10 MB fixes both: it uploads in seconds and previews on the first click.
Does Slack compress videos automatically?
No. Slack stores and streams whatever you upload at its original bitrate and only generates a thumbnail preview. That is the opposite of chat apps that re-encode on send, and it is exactly why compressing before you post matters: what you upload is what your whole team streams.
Will a 10 MB video look good enough for work?
For most clips, yes. 10 MB comfortably holds 60–120 seconds of clear 720p, and screen recordings — mostly static frames that H.264 compresses very efficiently — often fit several minutes at 1080p with no visible loss. For long, high-motion footage, trim it first or accept softer results.
What formats can I upload, and what do I get back?
You can drop in MP4, MOV, WebM, or MKV. The output is always MP4 with H.264 video and AAC audio — the most compatible combination and the one Slack plays inline on web, desktop, and mobile without asking anyone to download it first.