Video Compressor

About the Video Compressor

Shrink a video so it fits an upload or email limit, in one of three ways. Target size works out the bitrate from the length of the video: the size you choose, minus a small safety margin and the audio, divided by the duration — and lowers the resolution automatically when the bitrate would be too low for the original size. Quality keeps the resolution and re-encodes at a level you choose, never above the original’s bitrate. Resolution caps the size and frame rate, for example 4K to 1080p.

The result is an H.264/AAC MP4, which plays everywhere; if your browser can encode them, AV1 (MP4) and VP9 (WebM) give better quality at the same size. You see the expected size before you start, the real before/after sizes afterwards, and both videos side by side. Everything is done on your device with the browser’s encoder — nothing is uploaded.

How the target size is calculated

File size ≈ (video bitrate + audio bitrate) × duration ÷ 8. The page keeps 3 % of your target in reserve for the MP4 index and encoder overshoot, reserves 16 KB for headers, gives the audio 96–128 kbps (or keeps the original audio if it fits), and gives the rest to the video. If that leaves fewer bits per pixel than the codec needs to look clean (about 0.05 bits per pixel per frame for H.264), it picks a lower resolution — you can override this.

Browsers’ encoders work in a single pass, so the result can land a few percent above or below the target; the page shows the expected size as ±10 %. If the file comes out too big, it can re-encode once with a corrected bitrate (on by default).

Which format should I choose?

• MP4 · H.264 — plays on every phone, computer, TV and app. The safe choice for sending.
• MP4 · AV1 — noticeably better quality at the same size; plays in current browsers, recent Android phones and newer computers and TVs, but not on many older devices.
• WebM · VP9 — efficient and widely supported on the web and Android; less suitable for iPhones and editing apps.

Only formats your browser can encode are offered.

Common size limits

Gmail lets you attach up to 25 MB in total per email (Gmail Help, “Attachment size limit”); larger files are sent as Google Drive links instead. Messaging apps, chat services and forms set their own limits and change them from time to time, so check the current limit of the service you are sending to and type it in. Sizes on this page are decimal (1 MB = 1,000,000 bytes), which is how such limits are stated and slightly smaller than the binary megabytes (MiB) some file managers show, so a file that meets a target here also fits under the same number of MiB.

Limitations

• Compressing always re-encodes, so some detail is lost; very small targets for long videos look blocky. Trimming the video first (see the Video Trimmer) keeps more quality.
• Target-size results are approximate (single-pass encoders); expect within about ±10 %.
• Audio is never compressed below 96 kbps AAC (64 kbps Opus in WebM), because some browsers’ AAC encoders refuse lower rates.
• HDR videos become standard dynamic range (SDR) when re-encoded.
• The title and recording date are kept and portrait videos stay the right way up; other metadata, such as the phone model and the location, is left out of the compressed file.
• Re-encoding speed depends on your device; long 4K videos can take a while on phones. Without “Save straight to a file” (Chrome/Edge on a computer) the result is held in memory.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.