转换 WEBM 转 VTT

WEBM is an open, high-quality video standard that is usually used for delivering online videos using the HTML tag. WEBM is a container file format: the video stream is usually compressed with the VP8 codec and the audio stream is compressed with the Ogg Vorbis codec. The WEBM container format itself is based off of the popular Matroska container (MKV files). Since WEBM is an alternative to the patented H.264 and MPEG4 formats and widely supported by most major web browsers, it is used in both commercial and non-commercial applications.
The WEBM file format was created by Google to store video content and implement compression standards optimized for video streaming over broadband and mobile internet connections. Thus, royalty-free video compression technologies were used (VP8/VP9 and Ogg Vorbis). In addition, WebVTT subtitle tracks can we included within a WEBM file. WEBM files are also widely supported by Chrome, Safari, Firefox, and Internet Explorer.