media file converter
Media converters deal with clips that are in the wrong format or the wrong size for where they are going: a podcast recorded as video, a lecture too large to email, a short scene that has to loop silently in a post. Students, podcasters and social media managers are the usual users. mp4 to mp3 extracts the soundtrack from a video and leaves you with an audio file a fraction of the size, which is the right tool for turning a recorded talk into something you can listen to on a commute. mp4 to gif does the opposite kind of reduction, converting a few seconds of footage into a short looping animation that plays inline anywhere an image does. When the format is already right but the file is too heavy, the video compressor lowers the bitrate and resolution to fit a sharing limit while keeping the clip watchable. For changes to the content itself, the mp4 video editor covers trimming, joining and reordering scenes, and the mp3 editor cuts intros, silences and overlong pauses out of audio. A typical run is to edit first, then compress or convert last, so that you are not re-encoding material you were about to cut anyway.
5 tools available
Showing 1–5 of 5
mp3 editor
Trim audio on a waveform, add fades, adjust volume and export an MP3, all inside your browser.
mp4 to gif
Turn a clip from an MP4 into an animated GIF, choosing start time, length, frame rate, width and quality.
mp4 to mp3
Pull the audio out of an MP4 and save it as a 128, 192 or 320 kbps MP3 without uploading the file.
mp4 video editor
Trim, mute and resize MP4 files in your browser using FFmpeg.wasm, with no upload and no watermark.
video compressor
Shrink MP4, MOV and other video files in your browser using FFmpeg WebAssembly, with quality and size presets.
How the compression works in your browser
Quality is controlled by CRF, the constant rate factor. Instead of targeting a fixed bitrate, the encoder targets a constant perceived quality and spends whatever bits each scene needs. Lower CRF means higher quality and a larger file. For MP4 output the presets map to CRF 18 for Near Lossless, 23 for High Quality, 28 for Balanced and 35 for Max Compress. VP9 uses a different scale, so the WebM presets are 20, 27, 33 and 41 respectively.
MP4 output encodes video with libx264 using the fast preset. WebM output uses libvpx-vp9 with the bitrate set to zero so CRF alone governs quality, paired with Opus audio. Choosing a lower output resolution adds a scaling filter that reduces the frame height while preserving the aspect ratio.
Worked example: a 180 MB 1080p clip
The resolution change alone removes a large share of the data. A 1080p frame holds 1920 x 1080 = 2,073,600 pixels, while a 720p frame holds 1280 x 720 = 921,600. That is a 55.6 per cent reduction in pixels per frame before the encoder's own work begins.
On top of that, Balanced applies CRF 28 to the H.264 encode, a noticeably coarser quality target than most camera and screen-recorder output. A clip of this kind typically lands around 25 MB, which the tool reports as a saving of (1 - 25 / 180) x 100, about 86 per cent.
Choosing WebM instead at the equivalent Balanced setting of CRF 33 generally produces a smaller file again for similar perceived quality. Actual results vary enormously with content: a static screen recording compresses to a fraction of a handheld outdoor shot with moving foliage, because there is far less new information in each frame. Always check the reported sizes rather than assuming a ratio.
Choosing settings, and what to expect from the process
Pick MP4 when the file must play anywhere, including older phones, televisions and desktop media players, since H.264 is the most universally supported codec. Pick WebM when the destination is a modern browser and file size is the priority.
Be realistic about speed. Encoding in WebAssembly is slower than native FFmpeg, so a long or high-resolution video can take several minutes and will keep your processor busy. Leave the tab open while it works, and prefer a laptop on mains power for large files.
Two limits are worth knowing. Re-compressing a file that is already heavily compressed yields little and costs quality, since the detail has already been discarded. And the audio track is re-encoded too, so keep the original file if you may need it later.