Video Compressor & Trimmer

Email attachments cap out at 20–25 MB, free Discord and Slack channels reject bulky clips, and uploading a 200 MB phone video to a cloud compressor over slow Wi-Fi takes longer than the video itself. You can compress video online right inside your browser memory - choose Light, Balanced, or Maximum compression, downscale resolution to 1080p, 720p, or 480p, trim unwanted seconds off the ends, or strip the audio track without uploading a single frame.

Why smartphone and screen recordings weigh so much

Modern smartphones and desktop screen recorders prioritize zero-latency capture over file efficiency. A 45-second 4K or 1080p clip recorded on an iPhone or OBS often writes at 18 to 35 Mbps (megabits per second), producing a 100+ MB file even when the畫面 (screen) is mostly a static browser window or a talking head.

When you need to attach a bug reproduction video to a GitHub issue, send a product demo on Slack, or embed a background loop on a landing page, two adjustments cut 80% to 92% of that file weight with almost no visible difference on a laptop or phone screen:

1. Quantization / CRF bitrate optimization: Re-encoding the video stream with a higher Constant Rate Factor (CRF) allocates fewer bits to static background areas while keeping moving edges crisp.
2. Resolution downscaling & audio stripping: Dropping a 4K screen capture to 1080p or 720p reduces the total pixel count per frame by 4x to 9x, and muting the audio track on a silent bug-report screen recording removes an extra 128–192 kbps of unused audio data.

How to compress video online in your browser

1. Drop your video file (MP4, WebM, MOV, MKV, or AVI) into the upload zone or click Select Video to load it into the local preview player.
2. Choose a Compression Level (Medium / Balanced, High / Maximum Size Reduction, or Low / High Visual Fidelity) and a Target Format (MP4 H.264, WebM VP9, MOV, MKV, AVI, or Animated GIF).
3. Select a Maximum Resolution (Keep Original, 1080p Full HD, 720p HD, 480p SD, or 360p Compact), optionally enter Trim Start (s) and Trim End (s) timestamps, or check Mute / Strip Audio.
4. Click Compress & Export Video, watch the real-time frame progress bar, compare the before-and-after byte telemetry, and click Download Compressed Video.

Controls that let you hit any file size target

Instead of locking you into a single preset, the workspace combines bitrate quantization, spatial scaling, temporal trimming, and container remuxing in one panel.

• Three tuned compression tiers: Switch between Low Compression (preserves fine grain at ~CRF 21), Medium Balanced (the sweet spot at ~CRF 26 that typically cuts 55%–75% of file weight), and High Compression (~CRF 32 for fitting long clips under strict 8 MB or 10 MB upload caps).
• Resolution downscaler (1080p / 720p / 480p / 360p): Automatically scales width and height proportionally (rounding to even pixel multiples required by H.264/VP9 macroblocks) while never upscaling a smaller video.
• Start and End timestamp trimmer: Why compress 30 seconds of setup fumbles at the start and end of a screen recording? Entering Start: 4s and End: 38s slices the stream before encoding, cutting both encoding time and output size.
• One-click Audio Track Remover: Strips the audio stream completely (-an) when sharing silent UI demos or website background loops.
• Side-by-side size & savings summary: Displays original size, compressed size, exact megabytes saved, and percentage reduction alongside an interactive output video player so you can verify quality before saving.

Worked example: shrinking an 84 MB bug-report screen recording under 8 MB

Suppose a QA engineer records a 52-second macOS screen capture (Checkout-Bug-Capture.mov, 2560 x 1440 resolution, 84.4 MB). They need to attach it to a Jira ticket and a Discord thread where the attachment limit is 10 MB.

Inside the compressor:

1. They watch the preview and see the actual bug happens between second 6 and second 41 (a 35-second window). They set Trim Start = 6 and Trim End = 41.
2. They set Compression Level = Medium (Balanced), Target Format = MP4 (H.264), and Resolution = 720p (1280 x 720).
3. Because the screen recording has no voiceover - only accidental keyboard clicks picked up by the laptop mic - they check Remove Audio Track.
4. Clicking Compress & Export Video transcodes the 35-second 720p stream locally. The output Checkout-Bug-Capture-compressed.mp4 weighs 6.85 MB - a 91.9% size reduction that uploads to Jira and Discord in two seconds and plays inline on every desktop and mobile browser.

Performance tips and browser WebAssembly limits

Because video transcoding runs inside your browser CPU using WebAssembly (FFmpeg.wasm / MediaRecorder hardware pipelines) rather than on a remote GPU server farm, processing speed depends on your device's processor and the resolution you pick:

• Downscaling to 720p or 480p speeds up encoding by 3x to 5x: Encoding 1280 x 720 frames requires processing 921,600 pixels per frame instead of 8,294,400 pixels per frame in 4K.
• Trim first: Setting Trim Start and Trim End before clicking Compress means the encoder only processes the seconds you actually keep.
• Recommended file size ceiling: Desktop browsers comfortably handle source videos up to 500 MB – 1 GB. On mobile phones with tighter per-tab RAM sandboxes, stick to clips under 200 MB or under 3 minutes in length.

Privacy for private videos and internal screen recordings

Internal product demos, unreleased app walkthroughs, medical clips, and personal family videos never leave your device. All frame decoding, scaling, and encoding happen inside local browser memory with zero cloud storage.

How CRF (Constant Rate Factor) and resolution scaling interact

Understanding the two main levers in video compression helps you shrink files by 70–85% without turning faces or screen text into blocky mush:

• Constant Rate Factor (CRF / Bitrate control): Instead of forcing every second of video to use the exact same bitrate, perceptual encoding allocates more bits to fast-moving action scenes and far fewer bits to static talking-head or slide frames.
• Downscaling 4K (3840 × 2160) to 1080p (1920 × 1080) or 720p (1280 × 720): A 4K frame contains 8.29 million pixels—four times as many pixels as a 1080p frame (2.07 million) and nine times as many as a 720p frame (0.92 million). When sharing a clip on Discord, Slack, or mobile WhatsApp where viewers watch on a 6-inch screen, scaling a 4K phone video to 1080p or 720p reduces file size dramatically while looking sharper than an over-compressed 4K stream.

Related video and media tools

Need to convert between containers or extract an MP3/AAC audio track from a video? Open the Video Converter. To turn a short video clip into a looping animated image with text captions, use the Animated GIF Maker, burn a logo onto your clip in the Watermark Studio, or read our full guide on how to compress video locally in your browser.