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How to Crop Black Bars from a Video Online

Crop black bars from MP4, MOV, or WebM online. Identify letterboxing, calculate crop dimensions, avoid stretching, and export with HappyConvert.

How to Crop Black Bars from a Video Online

Crop black bars from MP4, MOV, or WebM online. Identify letterboxing, calculate crop dimensions, avoid stretching, and export with HappyConvert.

The short answer: crop the bars, do not stretch the picture

To crop black bars from a video online, first confirm that the bars are baked into the video itself. Then reduce the crop height for bars at the top and bottom, or reduce the crop width for bars on the left and right. Center the crop so the actual picture remains balanced.

HappyConvert performs this crop locally in the browser and exports a new MP4. Because cropping changes the frame dimensions, FFmpeg WebAssembly must re-encode the video. Processing time depends on duration, resolution, CPU speed, and available browser memory.

Are the black bars inside the file or added by the player?

Pause the video and capture a frame or inspect it in more than one player. If the same black pixels appear in the exported frame and every player, they are probably part of the file. This is common when a widescreen film is exported inside a 16:9 frame or a vertical phone clip is saved inside a horizontal canvas.

If the bars change when you resize the player window, they may be player padding. Cropping the file cannot force every website to use the same player shape. In that case, match the destination platform's aspect ratio instead of cutting pixels blindly.

How to calculate a centered crop for black bars

Start with the source width and height shown after loading the file. For a 1920 × 1080 video with 140-pixel bars at both the top and bottom, the visible height is 1080 - 140 - 140 = 800 pixels. Use a crop of 1920 × 800 with X at 0 and Y at 140.

For a 1920 × 1080 video with 240-pixel bars on both sides, the visible width is 1920 - 240 - 240 = 1440 pixels. Use 1440 × 1080 with X at 240 and Y at 0. Use even-numbered dimensions where possible because common H.264 pixel formats behave more reliably with even width and height.

Cropping, resizing, and changing aspect ratio are different jobs

Cropping removes rows or columns from the frame. If you crop 140 pixels from the top and 140 from the bottom of a 1920 × 1080 source, the result is 1920 × 800. The people and objects in the remaining area keep their original shape because the pixel geometry has not been stretched.

Resizing changes the number of pixels in the remaining frame. It can be useful after cropping when a website requires a maximum width, but it is a separate decision. Stretching a 1920 × 800 crop back to 1920 × 1080 changes the proportions and makes the picture look too tall.

Changing aspect ratio may involve cropping, padding, or both. A 2.40:1 movie frame does not become a natural 16:9 image just because the output box says 16:9. To fill that frame without bars, you must accept losing some picture at the left and right edges.

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