feature: add webm as an option in ffmpegCommandSetContainer #855
Description
When setting container format your choices are either mkv or mp4.
It would be great if we also could choose webm.
webm is an open contianer format. a simplified version of mkv with fewer codecs supported (it only supports modern open source patent free codecs) and a little smaller file size compared to mkv.
when forcing conform you need to drop data just like in mkv.
if you want to get fancy you can include a -c:s webvtt when force conform is checked to also convert the subtitles to webm's only supported subtitle format: webvtt. which was extended from srt to add optional fancy visual and color effects to the subtitles.
but that is not necessary and can be left to the user. just copy the mkv code and rename mkv to webm would suffice
other than that it can be treated just like an mkv file.