M2V is a video category file format, also called MPEG-2 Video. It supports video with a tighter time constraint and interlaced display. The encoded speed at which data is transmitted may be of the order of 40 Mbps (for storage and transmission). It may be higher for professional use in video production. Large frame sizes do not support HD resolution. MPEG-2 format is compatible with MPEG-1. The MPEG-2 format is used mainly for the consumer level of video broadcasting - for example, DVB. And for storage - for example, DVD. But they are also used for professional applications. Say for storing video in a studio. Files with the extension .m2v are necessary if you are preparing a video for burning to DVD using specialized programs. There will be no sound in such a file. This encoding method also involves the .m2a file, where the sound is stored. Then this pair of files (.m2v and .m2a) will be sent to the authoring program line. The program will output them without recoding in the program stream (MPEG 2 PS). There is one caveat. When the weight of these files is 4.3 GB or more, then you need to transcode this file and reduce the bitrate. So when you create * .m2v, you must first select the correct bitrate.
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.