How to shrink a video under Slack's upload limit on a Mac

Slack’s per-file upload ceiling is 1 GB, so if a video is being rejected the cause is usually something else: a workspace owner has restricted uploads, the connection dropped mid-transfer, or the file is in a format Slack will not preview. That said, a 600 MB screen recording in a channel is a burden on everyone who opens the thread, whether or not it is allowed. Trim it, export it at 1080p or 720p, or let Manatee’s Shrink mode land it under a size you choose, and it will upload in seconds and play inline.

What Slack’s limit actually is

Slack applies the same 1 GB cap to every plan. What varies is around it: workspace owners on paid plans can restrict which members may upload and which file types are allowed, the free plan hides messages and files older than its history window, and some corporate workspaces route uploads through a compliance tool with its own rules. If an upload fails repeatedly and the file is nowhere near 1 GB, ask an admin before you spend time compressing.

The more useful target is not the cap but the experience on the other end. Slack generates an inline player for video it can decode, and a file that streams instantly gets watched; one that needs a 400 MB download gets skipped. In practice, staying under about 50 MB keeps a clip snappy for everyone, including people on the mobile app. Slack, Teams and Discord file size limits has the current figures for all three, since the limits are checked and updated there.

Why your screen recording is so large

The videos that hit Slack are overwhelmingly screen recordings, and the Mac’s built-in recorder (Shift-Command-5) is generous. It captures at the full Retina resolution of the display, often 2880x1800 or larger, at 60 frames per second, with a high bitrate chosen to keep text crisp. That is the right choice for a master copy and the wrong one for a two-minute walkthrough of a bug. A recording can easily run 100 MB per minute.

Three dials bring it down, and bitrate, resolution and frame rate explains which to turn first. For screen recordings the order is: drop the frame rate to 30, bring the resolution down to 1080p, then lower the bitrate.

Trim first

1. Open the recording in QuickTime Player.
2. Choose Edit, Trim. Drag the yellow handles to cut the fumbling at the start and the “okay so that’s it” at the end.
3. Click Trim, then File, Save.

Half of most screen recordings is setup. Cutting it is free.

Export with QuickTime Player

1. Choose File, Export As.
2. Pick 1080p if there is text to read, 720p if the content is mostly visual.
3. Save. QuickTime writes a .mov, which Slack previews and plays inline without trouble.
4. Check the size in Finder. For a 2-minute recording, 1080p typically comes out between 20 and 60 MB depending on how much moves on screen.

This re-encodes the video, so do it once from the original. If the result is still too large, do not export the export; go to Manatee with the original instead.

Name the size with Manatee

When the brief is “under 50 MB” or “under 25 MB so the client’s mail server also takes it,” Shrink mode saves the guessing.

1. Open Manatee. Every feature is free for 24 hours with no account, then $9 once.
2. Drag the trimmed recording onto the menu bar icon or into the window’s drop zone.
3. Choose Shrink and enter a size in MB, say 45 for a 50 MB target.
4. The job list shows progress; the shrunk file is written beside the original, which Manatee never modifies.
5. Open the result and scrub through it. Text should still be legible at the size people will view it; if it is not, the number was too aggressive for the length, and trimming is the next lever.

If the recording came from a tool that produces MKV or WebM, or from a phone as HEVC, Slack may upload it but decline to play it inline, showing a bare download link. Convert it to MP4 in Manatee first; MP4 is the container Slack previews most reliably. Manatee is not an editor, so crop, annotate, and blur sensitive fields before this step, in the app that made the recording.

Alternatives to uploading the file at all

• Slack clips. The microphone and camera icons in the message box record audio and video inside Slack, up to a few minutes, with no file handling.
• A shared link. For anything long or for a series of recordings, upload once to the team’s cloud storage and paste the link. Slack unfurls it, nobody downloads anything they did not ask for, and you can replace the file later without re-posting.
• A GIF for short loops. A five-second “click here, then here” plays automatically in the thread. Keep it under ten seconds, though, or the GIF will be larger than the video was.

Questions

Slack says the upload failed but the file is only 200 MB. What is wrong?

Probably not the size. Check whether your workspace restricts uploads (an admin can tell you), whether the connection dropped, and whether the file opens at all on your Mac. A video that QuickTime refuses will often fail to upload cleanly; how to check whether a video file is corrupted walks through that.

Does Slack compress the video I upload?

It stores what you send and generates previews from it; it does not re-encode your file the way messaging apps do. The size you upload is the size everyone downloads, which is the argument for shrinking before you post.

What resolution should a screen recording be for Slack?

1080p for anything with code or text, 720p for everything else. The Slack window on a laptop is rarely wider than that, and the mobile app is narrower still.

Is MOV fine or should it be MP4?

Both play inline. MP4 is the safer bet if anyone on the team is on Windows or opens files outside Slack.