burnCDDA is a console frontend to cdrdao, cdrecord, MPlayer, mpg321, oggdec, mppdec, flac, normalize, and mp3_check. It can be used to create audio CDs from an M3U playlist (the playlist format of XMMS and amaroK) or from files inside a directory. It supports MP3, OGG Vorbis, Musepack, FLAC, WMA, M4A, and WAV files, and it might be the easiest way to copy an audio CD.
libsndfile is a C library for reading and writing sound files such as AIFF, AU, WAV, and others through one standard interface. It can currently read/write 8, 16, 24 and 32-bit PCM files as well as 32 and 64-bit floating point WAV files and a number of compressed formats. It compiles and runs on *nix, MacOS, and Win32.
SoX is the Swiss Army knife of sound processing tools: it can convert sound files between many different file formats and audio devices, and can apply many sound effects and transformations, as well as doing basic analysis and providing input to more capable analysis and plotting tools.
Mjpeg tools is a suite of programs which support video capture, basic editing, playback, and compression to MPEG-1/2 of MJPEG video. The capture software allows MJPEG video streams in AVI, Quicktime, and movtar format to be produced using the Iomega Buz, Miro DC10+, Matrox Marvel, and similar hardware. The editing and playback tools are hardware independent, with support for hardware accelerated playback if present. The MPEG compression tools are based on MPEG Software Simulation Group's reference encoder with enhancements to provide far faster compression and significant quality improvements.
tovid is a suite of command line utilities (and a graphical frontend) for creating video discs in DVD, VCD, SVCD, and KVCD/KDVD formats (PAL or NTSC). tovid supports a wide variety of input video formats, and can encode to several different output resolutions. Discs may be authored with hierarchical menus for navigation and playback.
mpg321 is a Free clone of mpg123, a command-line MP3 player. It is designed to be a drop-in replacement for mpg123, and therefore its interface has been designed around that of mpg123, without using any of its code. mpg321 has been designed for use with frontends such as gqmpeg, although it is just as useful on the command-line. Unlike mpg123, it supports ESD and ALSA output without recompiling, and it does all MP3 decoding with only fixed-point math by using the mad MPEG audio decoder library.