F4V is a well-known flash video format developed by Adobe System. It is supported by Adobe Flash Player. Currently, approximately 80% of online videos are transmitted using Adobe Flash technology. Files with the F4V extension are called a container format. The F4V format, in comparison with other files of the FLV category, uses boxes to store information. In addition to devices with an operating system from Apple, these files can play almost all browsers that support flash video playback. F4V files resemble .FLV files, but use “blocks” to store data. Examples of blocks that are supported by the F4V format include meta block (metadata), moov block (file header), ftyp block (requested player tools), uda block (user data in free form), etc. The format container, in the development of which the ISO Media File Format was used, initially used the Quick Time Container Format from Apple. Compared to the old FLV format, the F4V format is fully compatible with the h.264 and ACC formats. This provides an opportunity to use other container formats.
AU is an audio file format created in Audacity. This is a free cross-platform program designed to edit audio files. AU format (Audio Units) was developed by Sun Microsystems. This format greatly simplifies the task of reliable storage of audio files. An AU file consists of 3 parts: a header (max. 24 bytes), a description block of various sizes, and audio data. The file format is used on computers running the Sun or Unix operating system. However, it opens with other audio players. The AU format uses the logarithmic encoding method, previously very popular on computers running the Sun SPARCstation operating system. Previous sound file formats, in order to reduce the size, used the logarithmic scale of recording samples. Among the representatives of such formats, the Sun AU group of formats, which are still in action, gained great fame. Problems with opening the AU file usually manifest themselves when there are no corresponding applications that would be installed on the PC. Applications that use .AU files are Apple QuickTime Player, Microsoft Windows Media Player, Real Player, Winamp, and other widely used audio players. And this is the vast majority of professional audio editors.