Video Converter

Choose MP4 and leave Method on Auto. A MOV from a phone or camera almost always holds H.264 video and AAC audio, both of which MP4 accepts, so the streams are copied into the new container rather than decoded and compressed again. The plan panel will say "Copy" for both, and the finished file is identical in quality to what you started with — it just takes seconds.

Pick MP4 and check the plan. When the MKV holds H.264 or HEVC video, MP4 accepts it and the video is copied straight across; the audio is copied too unless it is something MP4 refuses, such as Vorbis or DTS, in which case only the sound is re-encoded to AAC. Bear in mind that only the first video and audio track come over, so an MKV carrying several language tracks or subtitles will arrive simplified.

Only when something is actually re-encoded. A stream copy moves compressed data unchanged, so the result is identical to the source and no setting can improve or degrade it. A re-encode decodes the picture and compresses it again, which always loses something, however small. The plan tells you which of the two is about to happen, and Auto avoids the second whenever the format allows.

No. The engine is FFmpeg compiled to WebAssembly and it runs inside your browser tab. The file is read from disk into the tab's memory and the result is written back out as a download. Nothing about the file crosses the network, which you can confirm by watching the network panel while a conversion runs.

The container is the file format itself — MP4, MKV, WebM — and it holds streams plus the timing and index information that keeps them playable. The codec is how the picture and sound inside are compressed, such as H.264 or AAC. A player can support a container and still fail on what is inside it, which is why "my MP4 will not play" is a real and common problem, and why this tool reports both separately.

No, and it usually makes things worse. The extension is a label; the bytes inside are laid out according to the real container, so a player told to expect MP4 will look for structures that are not there and refuse the file. A conversion rewrites that structure properly. When the streams are compatible it is nearly as fast as renaming and, unlike renaming, it actually works.

MP4 with H.264 unless you have a reason not to: browsers, phones, editors, and upload forms all handle it, and most sources can be copied into it without re-encoding. Use WebM when you want an open format playing natively on a web page, MKV when you need a container that will take an unusual stream without touching it, and MOV with ProRes when the destination is an editing timeline.

Check what the plan said went inside it. An MP4 carrying HEVC plays on Apple devices and often nowhere else, and one carrying VP9 is a legal file that much software refuses — both are flagged before you convert. Switching Method to Re-encode with H.264 selected produces the combination that plays essentially everywhere, at the cost of a full encode.

Only the first audio track is carried over, so a file with several language tracks arrives with whichever one came first. If the output is silent instead, the likely cause is an audio codec the container refused — the plan panel names it and re-encodes to something the container accepts, which is normally all that is needed.

Because they are different kinds of job. MOV and MP4 both accept H.264, so the streams move across without being decoded. WebM accepts only VP8, VP9, and AV1, so an H.264 picture has to be fully decoded and encoded again — every frame, on one thread, inside a browser tab. The plan panel says which of the two you are about to do before you commit to it.

It can read all three and copy any of them into a container that accepts them, since copying never decodes anything. It cannot produce them: this build has no AV1 encoder, its HEVC encoder does not run single-threaded, and its VP9 encoder fails with memory errors, so WebM is written as VP8. Re-encoding AV1 into something else is also out of reach, because decoding it needs hardware that WebAssembly cannot use. For HEVC and VP9 sources, converting to H.264 works normally.

A copy is quick almost regardless of length, because nothing is decoded — the limit is memory rather than time. A re-encode scales with the duration, the resolution, and your machine, and runs on a single thread, so a long high-resolution clip takes real time. The practical ceiling for either is around 250 MB, since the whole file is held in the tab while it works.