[Mplayer-cvslog] CVS: main/DOCS/tech formats.txt,NONE,1.1

[Arpi of Ize]

Update of /cvsroot/mplayer/main/DOCS/tech
In directory mplayer:/var/tmp.root/cvs-serv32764

Added Files:
	formats.txt 
Log Message:
extended ascii version of formats.html

--- NEW FILE ---
1. Input layer, supported devices, methods:
  - plain file, with seeking
  - STDIN, without seeking backward
  - network streaming (currently plain wget-like HTTP, no MMS support yet)
  - VCD (Video CD) track, by direct CDROM device access (not requires mounting disc)
  - DVD titles using .IFO structure, by direct DVD device access (not requires mounting disc)

2. Demuxer/parser layer, supported file/media formats:

  - MPEG streams (ES,PES,PS. no TS support yet)
    note: mpeg demuxer silently ignore non-mpeg content, and find mpeg packets
    in arbitrary streams. it means you can play directly VCD images (for example
    CDRwin's .BIN files) without extracting mpeg files first (with tools like vcdgear)
    It accepts all PES variants, including files created by VDR.
    Note: VOB (video object) is simple mpeg stream, but it usually has 01BD
    streams which may contain subtitles and non-mpeg audio. Usually found on DVD discs.
    
    Headers: mpeg streams has no global header. each frame sequecne (also called GOP,
    group of pictures) contains an sequence header, it describes that block.
    In normal mpeg 1/2 content there are GOPs of 12-15 frames (24/30 fps).
    It means you can freely seek in mpeg streams, and even can cut it to
    small parts with standard file tools (dd, cut) without destroying it.
    
    Codecs: video is always mpeg video (mpeg1, mpeg2 or mpeg4).
    audio is usually mpeg audio (any layer allowed, but it's layer 2 in most files)
    but 01BD streams may contain AC3 or LPCM too.
    
    FPS: mpeg2 content allow variable framerate, in form of delayed frames.
    It's mostly used for playback 24fps contant at 29.97/30 fps (NTSC) rate.
    (so called Telecine or 3:2 pulldown effect)
    It means you see 30 frames per second, but there are only 24 different
    pictures and some of them are shown longer to fill 30 frame time.
    If you encode such files with mencoder, using -ofps 24 or -ofps 23.98
    is recommended.

  - AVI streams.
    Two kind of RIFF AVI files exists:
    1. interleaved: audio and video contant is interlaved. it's faster and
       requires only 1 reading thread, so it's recommended (and mostly used).
    2. non-interleaved: audio and video aren't interleaved, i mean first come
       whole video followed by whole audio. it requires 2 reading process or
       1 reading with lots of seeking. very bad for network or cdrom.
    3. badly interleaved streams: mplayer detects interleaving at startup and
       enables -ni option if it finds non-interleaved content. but sometimes
       the stream seems to be interleaved, but with bad sync so it should be
       played as non-interleaved otherwise you get a-v desync or buffer overflow.
    MPlayer supports 2 kind of timing for AVI files:
    - bps-based: it is baed on bitrate/samplerate of video/audio steram.
      this method is used by most players, including avifile and wmp.
      files with broken headers, and files created with VBR audio but not
      vbr-compliant encoder will result a-v desync with this method.
      (mostly at seeking).
    - interleaving-based: note: it can't be used togethwer with -ni
      it doesn't use bitrate stuff of header, it uses the relative position
      of interleaved audio and video chunks. makes some badly encoded file
      with vbr audio playable.

    Headers: AVI files has a mandatory header at the begin of the file,
    describing video parameters (resolution, fps) and codecs. Optionally
    they have an INDEX block at the end of the file. It's optional, but
    most files has such block, because it REQUIRES for seeking.
    Btw usually it can be rebuild from file content, mplayer does it with
    the -idx switch. Mplayer can fix broken index blocks using -forceidx.
    As AVI files needs index for random access, broken files with no index
    are usually unplayable.
    Of course, cutting/joining AVI files needs special programs.

    Codecs: any audio and video codecs allowed, but I note that VBR audio is
    not well supported by most players. The file format makes it possible to
    use VBR audio, but most players expect CBR audio and fails with VBR,
    as VBR is unusual, and Microsoft's AVI specs only describe CBR audio.
    I also note, that most AVI encoders/multiplexers create bad files if
    using VBR audio. only 2 exception (known by me): NaNDub and MEncoder.
    
    FPS: must be constant, but skipping frames are allowed.

  - ASF streams:
    ASF (active streaming format) comes from Microsoft. they developed two
    variant of ASF, v1.0 and v2.0. v1.0 is used by their media tools (wmp and
    wme) and v2.0 is published and patented :). of course, they differ,
    no compatibility at all. (it's just a legality game)
    MPlayer supports only v1.0, as nobody ever seen v2.0 files :)
    Note, that .ASF files are nowdays come with extension .WMA or .WMV.

    Headers: Stream headers (codecs parameters) can be everywhere (in theory),
    but all files i've seen had it at the beginning of the file.
    Asf uses fixed packet size, so it is seekable without any INDEX block,
    and broken files are playable well.
    
    Codecs: video is mostly microsoft's mpeg4 variants, MP42, MP43 (aka DivX),
            WMV1 and WMV2. but any codecs allowed.
            audio is usually wma or voxware, but any codecs allowed.

    FPS: no fixed fps, every video frame has an exact timestamp instead.
    I've got stream with up to 3 sec frame display times.

  - QuickTime / MOV files:
    They come from Mac users, usually with .mov or .qt extension, but as
    MPEG Group choose quicktime as recommended file format for MPEG4,
    sometimes you meet quicktime files with .mpg extension.
  
    At first look, it's a mixture of ASF and AVI.
    It requires INDEX block for random access and seeking, and even for
    playback, like AVI, but uses timestamps instead of constant framerate
    and has more flexible stream options (including network stuff) like ASF.
    
    Headers: header can be placed at the beginning or at the end of file.
    About half of my files has it at the begining, others has it at the end.
    Broken files are only playable if they have header at the beginning!
    
    Codecs: any codecs allowed, both CBR and VBR.
    Note: most new mov files use Sorenson video and audio, they are
    patented, closed, secret, (TM)-ed etc formats, only Apple's quicktime
    player is able to playback these files (on win/mac only).

  - VIVO files:
    They are funny streams. They have a human-readable ascii header at
    the beginning, followed by interleaved audio and video chunks.
    It has no index block, has no fixed packetsize or sync bytes, and most
    files even has no keyframes, so forget seeking!
    Video is standard h.263 (in vivo/2.0 files it's modified, non-standard
    h.263), audio is either standard g.723 or Vivo Siren codec.
    
    Note, that microsoft licensed vivo stuff, and included in their netshow
    v2.0 program, so there are VfW/ACM codecs for vivo video and audio.