HEVC or h.265 is the most advanced codec for now because it has the lowest bitrate without losing the image quality. The codec has three main features that distinguishes it from others: parallel decoding, random access to images within the video stream and larger maximum block size. HEVC is aimed to offer the same level of video quality as AVC (h.264), but with improved compression, that is why a video file compressed with the codec will be twice smaller.

OGA is an audio extension for OGG file and it was developed by Xiph.Org Foundation. OGG is an open container format designed for streaming and may contain independent video, text and audio files. To open OGA, you need either to install an appropriate software like Vorbis, or to convert the file to a more common format.