4chan webm converter

How do I make a webm for 4chan?

1. Drop a video onto the File box at the top of the page, or click the box to pick one.
2. Choose the board you're posting to. "All boards" makes a file that every board accepts.
3. If the video is longer than the board allows, drag the trim handles to choose which part to keep.
4. Press "Convert to webm", then download the finished file and post it.

What are 4chan's webm limits?

On most boards a webm can be up to 4 MB and 120 seconds long, with no sound. Some boards are more generous:

• /wsg/: up to 6 MB and 400 seconds, with sound
• /gif/: up to 4 MB and 300 seconds, with sound

Every board takes VP8 or VP9 video with Opus or Vorbis audio, up to 2048×2048 pixels.

Can I post a webm with sound on 4chan?

Yes, on boards that allow it, such as /wsg/ and /gif/. Most boards reject a webm that has an audio track, so the "All boards" preset removes it. To keep the sound, pick /wsg/ or /gif/ as the board.

Are my videos uploaded anywhere?

No. The conversion runs on ffmpeg compiled to WebAssembly (ffmpeg.wasm), right in your browser, so your video never leaves your device. It's free, with no sign-up and no watermark.

How do I convert a GIF to webm for 4chan?

The same way as any other video: drop the GIF in and convert it. A webm is usually a fraction of the size of the same animation as a GIF, so GIFs that are too big to post often fit easily. GIFs have no sound, so the webm can go on any board.

Why does my webm look blurry?

The file has to fit a fixed size, so the longer the clip, the less data each second gets: a 120-second clip in 4 MB leaves only about 280 kbps. When that's too little for the video's resolution, the converter scales it down instead of letting it turn blocky. For a sharper result, trim the clip to just the part you need, or drop the audio.

Which video formats can I convert?

MP4, MOV, MKV, AVI, WMV, FLV, MPEG-TS, GIF and existing webm files — practically anything ffmpeg can read. Videos larger than 2048×2048 pixels are scaled down to fit 4chan's resolution limit.

Why VP8 instead of VP9?

4chan accepts both. VP9 compresses better, but its encoder currently crashes in the WebAssembly build of ffmpeg, so this converter uses VP8 with two-pass encoding to get the most out of the size limit, and Opus for audio.