amp-0.7.6.rar_MP3解码_amp open source mp3_linux mp3_mp3解码器

LINUX REALTIME AUDIO PLAYBACK Thomas M. Sailer sailer@ife.ee.ethz.ch Typical Unix schedulers go to great lengths to allow batch processing jobs to run on a machine while still providing interactivity. They do it by enhancing the priority of short bursty tasks. While this works well for many important tasks (such as X, xterm and compiling new kernel releases :-)), it does not fit the behaviour of a MPEG player. The tasks of a MPEG player have a "soft" deadline; if it is not met, no nuclear power plant blows up, but still it can be heard as an annoying artifact. That's what the POSIX.1b realtime scheduling extensions promise to remedy. rtbuf.c is an implementation of a buffering scheme using the POSIX realtime features. Its aim is to provide smooth playback of MPEG audio streams even on a very heavily loaded machine. It uses many advanced features of the operating system: - System V shared memory - POSIX.1b realtime scheduling extensions - POSIX.1b memory locking - Sound Driver DMA buffer mapping into the user proces space Make sure that you have enabled these features! The downside of these features is that they can only be used if the process has root permissions. Using realtime features is somewhat dangerous, since a realtime process can eat all the CPU time, rendering the machine unresponsive. So don't try this on your server! This implementation creates three processes: - The command line parse/control process. It runs continuously as root. - The MPEG decode/playback process. It revokes root rights as soon as it has enabled the realtime features, to minimize the risk for a security hole - The prefetch process. Its only purpose is to load the input file into a memory region shared with the decode process. It also revokes root rights. The MPEG decode process writes its output data directly into the soundcard DMA buffer, which is mmap'ed into process memory. This minimizes operating system overhead. To use this: Type ./configure --enable-realtime make chown root.root amp chmod u+s amp This buffering only works on Linux (maybe also on FreeBSD, but I don't know...) Other operating systems do not (yet) support the required features. A warning: The buffering might not work on an SMP system. This could be solved by making the macros atomic_set and atomic_read SMP safe. Have fun Tom