Convert AV1 to MKV

Not directly. AV1 plays inline in every browser; MKV does not, so a page embedding it falls back to a download link or an empty player frame. If the file is destined for a website, keep the AV1 for the web and treat the MKV as the archive or editing copy. MKV has almost no native hardware support — phones, browsers and TVs usually need VLC or a remux before they will play it.

It changes what to expect from the output file. One side of this conversion names an encoding rather than a wrapper, so what comes back is that bitstream inside whichever container suits it best — normally MP4 or MKV. The extension reflects the container; the codec is what actually determined the file size and where it will play.

Usually not. Most conversions keep one audio track, the one with the most channels (normally the main mix), re-encoded for the MKV container, so commentary and alternate-language tracks are dropped. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every track, and so does MP4 to MOV. To keep a different track, remux the AV1 with that track first (VLC or ffmpeg can do this), then convert it. MKV is Matroska, an open container designed in 2002 with no licensing restrictions and no ceiling on what it can hold.

On some pairs. MP4 to MOV keeps every text subtitle track. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every subtitle track: text subtitles are copied or converted to SRT, and picture-based subtitles such as DVD or Blu-ray ones are copied as they are. MP4, MOV and WebM to MKV keep only the first subtitle track (as ASS), and MP4 to WebM keeps the first one as WebVTT. Other pairs, including MKV to MP4 or MOV and WebM to MP4, drop subtitle tracks, and the converter does not burn them into the picture. Subtitles that are already burned in stay, because they are part of the video frames.

MKV is the only mainstream container that stores arbitrary attached files (TTF fonts for ASS subs, JPG cover art, fan-translated PDF inserts). Going from AV1 to MKV drops these attachments when MKV is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep AV1 as a backup if you depend on attached fonts.

It depends on the MKV container. MP4, MOV and MKV output use H.264, which plays on practically every phone, browser and TV. WebM output uses VP9. AVI, WMV and MPEG output use the older codecs those formats were designed for. MKV is the archival container of choice because it stores unlimited audio tracks, soft subtitles, chapter markers and cover art in one file.

There is no HDR processing or tone mapping. When the video stream is copied (MKV to MP4 or MOV with the default settings), HDR10 passes through as it is. When the video is re-encoded, the HDR10 mastering metadata is dropped and Dolby Vision or HDR10+ data is not kept, and with a Quality, Resolution or Frame Rate setting some pairs also reduce the video to 8-bit colour, so an HDR AV1 can look washed out in the MKV.

It depends on what happens to the video. MKV to MP4 or MOV with the default settings copies the video stream unchanged, so the size stays close to the source. Most other pairs re-encode it: a high-bitrate AV1 usually comes out smaller, while an already heavily compressed one can grow. Smaller File under Quality gives the smallest output, and H.265 in the Codec setting (MP4, MOV and MKV) is usually smaller than H.264 at similar quality but plays on fewer devices.

The converter has no resolution cap of its own; the limit is the upload size allowed on your plan, and 4K, 8K and 60 fps files keep their resolution and frame rate unless you change them. MKV to MP4 or MOV with the default settings copies the video stream, which is quick at any resolution. Other pairs re-encode on CPU and the time grows with the pixel count, so a long 4K or 8K file takes much longer than the same length in 1080p.