Resize MP4
Changing a video's resolution means redrawing every frame at the new size, so it always involves a re-encode - there's no shortcut. The payoff is a much smaller file: going from 1080p to 720p roughly halves it. Drop a video here, choose 1080p, 720p or 480p under Resolution, and Wave scales it down, keeping its shape, and re-encodes it to H.264 in your browser.
What actually changes
Wave's resolution choices set the short side of the picture: 720p means 1280 x 720 for a landscape video and 720 x 1280 for a vertical one. The other side follows the original shape, rounded to an even number of pixels as H.264 requires, so nothing gets stretched or cropped. Only sizes smaller than the source are offered, because scaling up adds pixels without adding detail.
Each step down cuts the pixel count by more than half (720p has 44% of 1080p's pixels), and Wave sets the bitrate to match the new size: about 5 Mbps at 1080p, 1.9 Mbps at 720p and 1 Mbps at 480p for 30 fps video. A 4K phone clip resized to 1080p typically comes out at a fifth of the original size or less. Wave scales with a filter that takes the size ratio into account, so fine detail shrinks smoothly instead of turning into jagged edges.
Resizing combines with the other options. Set a file size too, and Wave fits the bitrate to the size you chose - or picks an even smaller resolution if the size demands it. Rotation and trimming apply in the same pass, and HDR clips are converted to standard colours as they're resized, so they don't come out washed out.
For exact dimensions that aren't a standard size, or for cropping to a different shape (like 4:5 for an Instagram feed post), use ffmpeg: `ffmpeg -i input.mp4 -vf "scale=-2:720" -c:v libx264 -crf 22 -c:a copy output.mp4` scales to 720 pixels tall with a matching even width, and `crop=w:h` cuts out part of the frame. HandBrake's Dimensions tab does both with a preview.
Three steps.
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Step 1
Drop the video onto Wave above. On this page, the Options panel opens on Resolution.
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Step 2
Choose 1080p, 720p or 480p. The plan shows the exact output size and the estimate updates.
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Step 3
Select Convert to MP4 and save the resized video.
Answers, specifically.
Which resolution should I choose?
1080p for anything watched on a TV or laptop, 720p for phones and messaging, 480p when the file has to be as small as possible. For a hard size limit, set File size instead and Wave picks the resolution for you.
Does resizing keep the shape of the video?
Yes. Wave scales both sides by the same amount, so a vertical phone video stays vertical: at 720p it becomes 720 x 1280.
Can I make a video bigger?
No. Wave only offers sizes smaller than the source, because scaling up can't create detail that wasn't recorded; it only makes the file bigger.
Does resizing affect the sound?
The audio is re-encoded to AAC along with the video, keeping its channel count, at 96 kbps per channel - enough that most people can't tell it from the original. To drop it, tick Remove the audio track.
Why do H.264 videos need even dimensions?
Because the colour information is stored at half resolution in both directions, so the picture has to divide evenly by two. Wave rounds the scaled size to even numbers automatically.
How long does it take?
Wave decodes every frame of the source in the browser, so a 4K source takes much longer than a 1080p one, whatever size you resize to. Trimming at the same time helps, because only the kept part is processed.