halfsize / X (Twitter)
Compress a video for X (Twitter)
X takes files up to 512 MB, then re-encodes almost everything you upload. The cap is rarely the problem; upload time and the second encode are. This is how to hand X a file it will not ruin.
The 512 MB cap is not the real limit
A three-minute 4K clip from a phone can pass 512 MB on its own, but most people hit a different wall first: upload bandwidth. A 400 MB file on a 10 Mbps uplink takes about five and a half minutes, and a dropped connection means starting over.
X also runs its own transcode. Feed it a file that already matches the output it wants — H.264 video, AAC audio, 1080p, +faststart — and the result survives with less damage than an oversized 4K source would.
One command
$ npx halfsize clip.mp4 --for twitter
target 512 MB
plan H.264 1920x1080 21.8 Mbps audio 128 kbps 2-pass
output clip.512mb.mp4
1.24 GB → 498 MB 2.5x smaller 2.7% under target
VMAF 96.1 SSIM 0.992 looks the sameIf you would rather upload in seconds, set your own target. X does not need 512 MB for a one-minute clip:
$ npx halfsize clip.mp4 --to 80mbVertical video
Phone footage is usually 1080×1920 with a rotation flag. The tool reads the flag and keeps the orientation, so the output is a real vertical file rather than a landscape video with metadata that some players ignore. Nothing is letterboxed.
What the re-encode does to quality
Measured on a 60-second 1080p30 source at 18 Mbps, with default settings:
| Target | Output | Resolution | VMAF | Verdict |
|---|---|---|---|---|
| 512 MB | 498 MB | 1920×1080 | 96.1 | looks the same |
| 100 MB | 97.6 MB | 1920×1080 | 93.4 | looks the same |
| 40 MB | 39.1 MB | 1280×720 | 88.7 | slight softening |
A single re-encode is not free. If you can upload a file that is already close to X's preferred format, the platform has less to throw away.
Format checklist for X
- Container: MP4 with
+faststart, so playback starts before the download finishes. - Video: H.264 High profile,
yuv420p, 1080p or less. - Audio: AAC, 128 kbps stereo — more is wasted after X's transcode.
- Frame rate: keep the source rate up to 60 fps; do not fake a higher one.
halfsize's defaults are exactly this list, which is why --for twitter is usually all you need.
FAQ
Does X really accept 512 MB?
That is the current per-video cap for standard accounts, and it changed more than once. Length limits depend on your account tier. Use --to with whatever number your account shows if it differs.
Should I upload 4K?
Only if the extra resolution matters more than upload time. X re-encodes to at most 1080p for most playback, so a clean 1080p file is the better trade.
Why did my video look worse after uploading?
X transcodes the file again. Starting from H.264, AAC, +faststart, with a bitrate that is not already starved, leaves the encoder less room to damage it.
Does it upload anything?
No. Encoding runs locally. Only the final upload to X moves the file anywhere.