No. ffmpeg.wasm runs inside your browser; videos never leave your device.

Why does resizing require re-encoding?

Each frame is encoded relative to a fixed resolution, so changing the resolution requires re-generating pixels — i.e. re-encoding. Stream copy can't do it.

Which CRF should I pick?

18 is visually lossless, 23 is the default, 28 still acceptable, higher gets noticeably blocky. Aim for 23–28 for streaming.

libx264 (H.264) outputs to mp4 for the broadest compatibility.

Back to Video

Video resize — change target resolution, keep aspect ratio

Resize a video to a target width with the height inferred from the aspect ratio. Re-encodes with libx264 (CRF adjustable) and outputs mp4. Supports batch processing and a single ZIP download.

videoresize

How to use

Drop video files. Pick a target width (preset or custom) and CRF (quality: 0 = lossless to 51 = worst, 18–28 recommended). Click Resize — ffmpeg.wasm re-encodes via libx264 to the target width (height inferred from aspect ratio) and outputs mp4. Batch processing and a ZIP download are supported.

FAQ

Are videos uploaded?: No. ffmpeg.wasm runs inside your browser; videos never leave your device.
Why does resizing require re-encoding?: Each frame is encoded relative to a fixed resolution, so changing the resolution requires re-generating pixels — i.e. re-encoding. Stream copy can't do it.
Which CRF should I pick?: 18 is visually lossless, 23 is the default, 28 still acceptable, higher gets noticeably blocky. Aim for 23–28 for streaming.
Why mp4 only?: libx264 (H.264) outputs to mp4 for the broadest compatibility.

Related tools

Video compress — shrink size, tune CRF / preset / x264

Re-encode a video with libx264 at the chosen CRF to shrink the file size while keeping the resolution. Pick a preset to trade speed for compression. Output is mp4. Supports batch processing and a single ZIP download.

videocompress

Video rotate — 90° / 180° / 270° clockwise (re-encoded)

Rotate a video by 90° / 180° / 270° clockwise. Powered by ffmpeg.wasm running in your browser — re-encoded with libx264 while preserving audio. Videos never leave your device.

videorotate

GIF to MP4 converter — H.264 cuts file size to 1/5–1/10

Convert animated GIFs to H.264/AAC MP4 videos. GIFs balloon quickly; MP4 (H.264) typically shrinks the file to 1/5–1/10 the size and plays inline on X (Twitter), Bluesky, Discord and other social platforms. ffmpeg.wasm runs entirely in your browser — GIFs never leave your device. Supports batch processing and a single ZIP download.

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Subtitle Converter

Convert subtitle files between SRT / VTT / ASS / SSA / SBV / SUB / SMI / LRC. Drop files and pick a target format — runs entirely in your browser via subsrt-ts (MIT). No uploads.

videoconversiontext