What does Video Resizer do?
Resize video in your browser for Reels, TikTok, Shorts, YouTube or feeds: 1080p, 720p, 480p, 1:1, 9:16 or 4:5 with bars, crop or stretch.
- Price
- Free
- Account
- Not required
- Processing
- Entirely in your browser; your data and files are not uploaded
- Works on
- Any modern browser on desktop, tablet or phone
- Category
- Video and Audio Tools
How to use the video resizer
- Drop a video (MP4, MOV, WebM, MKV or AVI, up to 300 MB).
- Pick an output size, such as vertical 9:16 for Reels, TikTok and Shorts, or enter a custom size.
- Choose how to fit: bars in a colour you pick, crop to fill, or stretch.
- Click Resize and download the MP4.
Worked example
A 1920 x 1080 video into 1080 x 1920 vertical
With bars, the video is scaled to 1080 x 608 (1080 / 1920 = 0.5625, and 1080 x 0.5625 = 607.5, rounded to an even 608) and centred with bars above and below. With crop to fill, it is scaled to 3413 x 1920 and the centre 1080 pixels of width are kept.
How it works
FFmpeg re-encodes with libx264 (-crf 23 -preset veryfast) into MP4. Fit with bars uses scale=W:H:force_original_aspect_ratio=decrease,pad=W:H:(ow-iw)/2:(oh-ih)/2:color=...; crop uses scale=W:H:force_original_aspect_ratio=increase,crop=W:H; stretch uses scale=W:H. setsar=1 keeps square pixels. AAC audio is copied unchanged; other audio is encoded to AAC.
Assumptions
- Phone videos with rotation metadata are rotated upright before resizing.
- Output dimensions are rounded to even numbers, which H.264 requires.
- Enlarging a small video does not add detail.
Frequently asked questions
Are my files uploaded?
No. The file is processed by FFmpeg compiled to WebAssembly, running inside your browser. Only the engine itself is downloaded (once, from cdn.jsdelivr.net); your video, audio or images never leave your device.
Which size should I use for Reels, TikTok and Shorts?
Vertical 9:16 at 1080 x 1920. Use crop to fill if the subject is centred, or bars if nothing may be cut off.
Does resizing reduce quality?
Every re-encode is lossy, though CRF 23 is a standard quality level. Downscaling also removes detail by design.
Why does the first run take longer?
The first time you use any of the video and audio tools, your browser downloads the FFmpeg engine, about 31 MB. It is stored in your browser, so later runs on this device start without downloading it again unless you clear site data.
Limitations
- FFmpeg runs as single-threaded WebAssembly in the browser, which is much slower than desktop FFmpeg. Processing time depends on the file length, resolution and your device; long HD videos can take many minutes.
- Browsers limit how much memory a page can use. Very long or high resolution files can fail with an out of memory message, especially on phones and tablets.
- Files up to 300 MB; custom sizes up to 3840 pixels per side.
- Output is MP4 only. Subtitles and extra audio tracks are not kept.