WebM is an video format which consists of VP8 video and Vorbis audio. It provides open video compression for HTML5 videos and most major web browsers support WebM as a part of HTML5 video delivery. WebM is an alternative to the patented h.264 and MPEG4 standards, and is suitable for commercial and non-commercial applications.
FLAC is a lossless audio file format. It is similar to MP3 format but the main difference between these 2 formats is FLAC file compress the file size without changing the quality of audio. It can compress an audio file up to half of its original size using lossless compression algorithm.