CONVERTIR
MP4 → WEBM

Only when it has to. If the codecs inside MP4 (usually H.264 or H.265 for video, AAC for audio) are accepted by WEBM, we stream-copy — the bytes are repackaged into the new container with zero re-encoding and no quality loss. When the source uses a codec the target does not support, we transcode at a matching bitrate to keep the visual quality close to the original.

Yes in Safari 14.1 and later (macOS Big Sur +, iOS 14.1+). For older Safari, serve an MP4 fallback via <source>. Modern devices from 2020 onward all support WebM natively.

With stream copy, expect the job to finish in seconds to tens of seconds regardless of video length — the work is mostly rewriting the container. Transcoding is slower (roughly real-time: a ten-minute clip takes about ten minutes) because every frame must be decoded and re-encoded. The progress bar shows which mode applies.

Using VP9 at matched quality, expect 30-50% smaller than the source MP4 with H.264. AV1 saves another 20-30% on top but requires longer encode times.

Yes. Resolution, frame rate, colour space and bit depth are preserved by default; stream copy is literally bit-identical on these parameters. If you explicitly pick a lower bitrate or a different codec in Advanced, the output is rebuilt to those settings, but the default is always "match the source".

Yes. The AAC audio from the MP4 is transcoded to Opus in the WebM at 128 kbps by default, which is perceptually transparent for speech and music.