Return to README CVS log

Up to [DVB] / libsoftmpeg

Annotation of libsoftmpeg/README, revision 1.2

1.1       hunold      1: libsoftmpeg
                      2: ===========
                      3: 
                      4: 1) The idea
                      5: -----------
                      6: 
1.2     ! hunold      7: Many people have recently decided to work on software only mpeg
        !             8: decoderes. The goal is to have a cheap DVB x86 box with vdr or MythTV
        !             9: on it, but only using a so-called budget DVB card without onboard mpeg
        !            10: decoder.
1.1       hunold     11: 
                     12: 2) The problems
                     13: ---------------
                     14: 
1.2     ! hunold     15: The "linuxtv-softmpeg" project tries to provide the "libsoftmpeg"
        !            16: library, a thin library on top of existing technologies that adresses
        !            17: the following problems:
1.1       hunold     18: 
                     19: - low-delay buffering (for fast channel switches)
                     20: - mpeg audio decoding
                     21: - audio and video syncronization 
                     22: - audio rendering
                     23: - video rendering
                     24: - long term playback stability
                     25: 
                     26: 3) Existing "solutions"
                     27: -----------------------
                     28: 
1.2     ! hunold     29: In the past, there have been different approaches to solve these
        !            30: problems, but they are not quite satisfying yet.
1.1       hunold     31: 
1.2     ! hunold     32: For example, while "mplayer" and "xine" are excellent movie players,
        !            33: they use huge buffers for buffering and therefore make channel
        !            34: switching nearly unbearable. Additionally, they lack long-term
        !            35: stability, because they don't synchronize to the incoming stream and
        !            36: buffer over- and underrums quite frequently occur. (see below for
        !            37: details)
        !            38: 
        !            39: The "softdevice" plugin from VDR is on the right way, but unfortunately
        !            40: it is bound to VDR. Other projects like "mythtv" and the like need to
        !            41: duplicate the code or invent the wheel again,
1.1       hunold     42: 
                     43: 4) libsoftmpeg
                     44: --------------
                     45: 
1.2     ! hunold     46: In order to use this project, you need: 
        !            47: 
        !            48: - DirectFB and a supported gfx
        !            49: adapter (cle266 or Matrox G200/4x0/5x0 is fine, vesafb is only enough
        !            50: if you have a horibbly fast machine ;-)
        !            51: 
        !            52: - FusionSound, which needs OSS or ALSA (with oss emulation) sound
        !            53: drivers
        !            54: 
1.1       hunold     55: - libavcodec, version 0.4.8 from http://ffmpeg.sf.net is fine
                     56: 
                     57: "libsoftmpeg" already does the following:
                     58: 
1.2     ! hunold     59: - low-delay buffering for audio and video, adjustable audio
        !            60: prebuffering (currently 500ms, channel switching is usually done in
        !            61: less than a second)
1.1       hunold     62: 
                     63: - mpeg audio decoding via libavcodec from "ffmpeg" project
                     64: 
                     65: - mpeg video decoding via libavcodec from "ffmpeg" project
                     66: 
1.2     ! hunold     67: - audio and video synchronization using a "sync-to-audio-pts" approach
        !            68: and "free flowing video display" (see below for a detailed description
        !            69: of my ideas)
        !            70: 
        !            71: - video rendering using DirectFB (http://www.directfb.org), a thin
        !            72: library ontop of the Linux framebuffer device. DirectFB hosts a
        !            73: "cle266" driver which drives the tv out of the EPIA/cle266 boards very
        !            74: well
        !            75: 
        !            76: - audio rendering using FusionSound
        !            77: (http://www.directfb.org/fusionsound.xml), a thin library on top of
        !            78: DirectFB and Fusion (fast interprocess communication), which supports
        !            79: sound mixing, pitch adjustment and other neat features. Sound mixing is
        !            80: very important, other applications can overlay system sounds onto the
        !            81: live tv audio.
1.1       hunold     82: 
                     83: 4) How to get it to work
                     84: ------------------------
                     85: 
1.2     ! hunold     86: All this is working fairly well, a demonstration application is
        !            87: included with the library that reads from the DVR device (so you need
        !            88: "szap" for example to tune to a service and have the data put to the
        !            89: DVR device) and displays audio and video. It should be easily possible
        !            90: to use "libsoftmpeg" in "vdr", too.
        !            91: 
        !            92: Please apply the "fusionsound_realtimepriority_reset_on_flush.diff"
        !            93: patch to FusionSound first via "patch -p0 < [...]) in the FusionSound
        !            94: directory and compile again. This adds realtime priority to the audio
        !            95: feeding thread. If you omit this, the audio thread might starve and
        !            96: sound will be jerky.
        !            97: 
        !            98: If you do a "./autogen.sh ; make install" you'll get a demo application
        !            99: called "dfb_ts", which reads a transport stream from the DVB dvr
        !           100: device. You need to tune your frontend with "szap" for example and
        !           101: redirect the data to the dvr device with the "-r" switch. For example:
1.1       hunold    102: 
                    103: > szap -r "Das Erste"
1.2     ! hunold    104: 
        !           105: Then you can start the demo application and provide the video and audio
        !           106: pids for the service you like to watch (have a look at "szap", it tells
        !           107: you the correct pids):
        !           108: 
1.1       hunold    109: > ./dfb_ts /dev/dvb/adapter0/dvr0 0x7ff 0x800
                    110: 
                    111: 4) The future
                    112: ------------------------
                    113: 
1.2     ! hunold    114: What's currently completely missing is long-term playback stability. As
        !           115: you probably know, the problem arises due to the different clocks used
        !           116: for dvb encoding and decoding. See below for a detailed description of
        !           117: the problem and my ideas on how it can be solved on x86.
        !           118: 
        !           119: The next major step would be to add the ideas of long-term playback
        !           120: stability and the cle266 mpeg decoder stuff to the library, so that
        !           121: EPIA users can use the hardware acceleration.
        !           122: 
        !           123: "IDEAS" contains a description of the concepts currently implemented
        !           124: for audio/video synchronization and the ideas for long-term playback
        !           125: stability.
1.1       hunold    126: 
                    127: 5) If you want to participate
                    128: -----------------------------
                    129: 
1.2     ! hunold    130: There is a mailing list for this project. Write a mail to
        !           131: <ecartis@linuxtv.org> with "subscribe linuxtv-softmpeg" in the subject
        !           132: to subscribe.