There are two different video file formats known as Flash Video: FLV and F4V. The audio and video data within FLV files are encoded in the same manner as they are within SWF files. The F4V file format is based on the ISO base media file formatand is starting with Flash Player 9 update 3.
Opus is a lossy audio coding format developed by the Xiph.Org Foundation and standardized by the Internet Engineering Task Force, designed to efficiently code speech and general audio in a single format, while remaining low-latency enough for real-time interactive communication and low-complexity enough for low-end ARM3 processors. Opus replaces both Vorbis and Speex for new applications, and several blind listening tests have ranked it higher-quality than any other standard audio format at any given bitrate until transparency is reached, including MP3, AAC, and HE-AAC.