A WebAssembly build of FFmpeg downloads the first time you use the tool, then runs entirely in your tab. Your file is read into JavaScript memory, transcoded locally, and returned as a downloadable blob — it never touches a server.

Cloud converters run on dedicated CPUs (and often GPUs) with native FFmpeg builds. WebAssembly runs in a single browser thread with no hardware encode acceleration, which is typically 3–8× slower than a native run. We trade that speed for total privacy: your file never leaves your device.

MP4 (H.264 + AAC) for universal compatibility, WebM (VP8 + Vorbis) for the open web, MOV (H.264 + AAC) for Apple workflows, and MKV (H.264 + AAC) as a flexible archival container.

Up to 500MB. Longer or higher-resolution clips use more browser memory; if you hit a memory error, lower the resolution first or convert in shorter segments using the Video Trimmer.

Pick the High quality preset for visually transparent results (CRF 20). Balanced (CRF 23) is the recommended sweet spot. Small (CRF 28) trades some quality for a much lighter file — useful for messaging or web embedding.

Yes — FFmpeg WASM decodes virtually every common codec (H.264, H.265, VP8/9, MPEG-2, MPEG-4, DivX, Xvid, Theora, FLV, etc.) and re-encodes to your chosen output, so legacy clips can be brought into modern formats.

Soft subtitles and chapter tracks are dropped during conversion because they are not universally supported across containers. Burn-in subtitles ahead of time with the Add Subtitles tool if you need them visible in the output.

No. The conversion is 100% client-side. We do not transmit, store, or log your video. Closing the tab erases the file from memory immediately.

It depends on whether the conversion is a container swap or a full re-encode. If you keep the same video and audio codecs and just change the container (e.g. MOV → MP4 with both already in H.264/AAC), there is zero quality loss — the file is essentially renamed at the codec level. If the codec changes, the conversion is a re-encode and adds a small generation of compression loss; at sensible bitrates this is invisible.

The container is the file format wrapper (MP4, MOV, MKV, WebM, AVI) — it organises how the video and audio streams sit inside the file. The codec is the algorithm that compresses the actual video and audio data (H.264, H.265, VP9, AAC, Opus). MP4 and MOV containers can hold the same H.264 video stream — converting between them is just renaming the wrapper. Converting between codecs is a full re-encode.

MP4 with H.264 video and AAC audio is the safest choice — it plays in every browser, every phone, every TV, every editing tool, and uploads to every social platform. WebM is great for the open web but not all editors handle it. MKV is the most flexible but rejected by some platforms and players. MOV is essentially MP4 with an Apple-leaning naming convention. AVI is a legacy format kept around for compatibility with old hardware.

Container-only swaps (same codecs) finish in seconds. Full re-encodes run at 1–3× real time on modern hardware — a 10-minute video takes 10–30 minutes. The tool shows you whether the conversion is a fast swap or a full re-encode before you start so you can plan accordingly.

Subtitle tracks and chapter markers are copied over when the destination container supports them. MKV supports the most metadata, MP4 supports most common things, WebM supports basic chapters. AVI does not support modern subtitles, so they are dropped if you convert to AVI.

Not directly with this tool — for audio extraction, use Audio Converter, which can pull audio out of a video file and convert to MP3, WAV, AAC, OGG or FLAC.

Most modern containers (MP4, MKV, MOV, WebM) support multi-channel audio, and the tool preserves the channel count by default. The exception is some legacy containers and some specific codec combinations — the tool warns you if your selected combination will downmix to stereo, so you can choose differently.

Usually because the chosen output codec is less efficient than the original, or because the bitrate was set higher than necessary. If size matters, use Video Compressor instead, which is specifically designed to produce smaller output files. The converter aims for transparent quality, not minimum size.