hvirtual/quicktime/docs/codecs.html

   1 <TITLE>Quicktime for Linux</TITLE>
   2
   3 <H1>Codec information</H1>
   4
   5 The following concerns all the codecs built into the library.<P>
   6
   7
   8 <H1>DIVX</H1>
   9
  10 This encodes video in MPEG-4 using the OpenDivx codec.  This is the
  11 preferred compressed format although it probably won't be supported by
  12 Microsoft or Apple any time soon.  It takes the following
  13 parameters:<P>
  14
  15
  16 <CODE>
  17 divx_bitrate (int)<BR>
  18 divx_rc_period (int)<BR>
  19 divx_rc_reaction_ratio (int)<BR>
  20 divx_rc_reaction_period (int)<BR>
  21 divx_max_key_interval (int)<BR>
  22 divx_max_quantizer (int)<BR>
  23 divx_min_quantizer (int)<BR>
  24 divx_quantizer (int)<BR>
  25 divx_quality (int)<BR>
  26 divx_fix_bitrate (int)<BR>
  27 </CODE><P>
  28
  29
  30 <H1>DV</H1>
  31
  32 DV is supported for full decoding but only for black and white encoding
  33 on IA-32 platforms/architectures.  Secondly, only NTSC 25 Mbit/sec
  34 4:1:1 DV data has ever been tested.  There are two derivatives of DV:
  35 <B>DVC</B> and <B>DVCP</B>.  Only DVC is currently supported.<P>
  36
  37 <H1>IMA4</H1>
  38
  39 The IMA4 compressor reduces 16 bit audio data to 1/4 size, with very
  40 good quality.  For many years IMA4 was the best compressed audio format
  41 in Quicktime.  The first Starwars trailer in 1998 was encoded using
  42 IMA4 audio.<P>
  43
  44 <H1>JPEG</H1>
  45
  46 JPEG is preferred for compressed video.  This format writes a seperate
  47 JPEG photo for every frame in YUV 4:2:0.<P>
  48
  49 JPEG supports the following parameters, which can be set after
  50 quicktime_set_video.<P>
  51
  52 <CODE>
  53 jpeg_quality  (int)<BR>
  54 jpeg_usefloat (int)<BR>
  55 </CODE><P>
  56
  57 These takes a quality factor from 1 - 100 and a booleen flag to
  58 determine whether floating point operations should be used to slow it
  59 down.<P>
  60
  61 <H1>MJPA</H1>
  62
  63 MJPA stores each frame as two JPEGs interlaced and in YUV 4:2:2.  The
  64 real advantage is that it can split compression and decompression
  65 across 2 processors and it supports higher color sampling than JPEG
  66 Photo.  To enable dualized MJPA processing call:<P>
  67
  68 <CODE>
  69 quicktime_set_cpus(quicktime_t *file, int cpus);<P>
  70 </CODE>
  71
  72 immediately after the <B>quicktime_init</B> call.  Cpus should contain
  73 the number of CPUs to devote to compression.<P>
  74
  75 After specifying MJPA in quicktime_set_video you need to call
  76 <B>quicktime_set_jpeg</B> as described previously.<P>
  77
  78 <H1>PNG</H1>
  79
  80 This consists of one PNG image for every frame.  Like <B>RAW</B> this
  81 codec supports 32 bit depths.<P>
  82
  83 <H1>RAW</H1>
  84
  85 RAW identifies both a video and an audio codec.  When you specify RAW
  86 for an <B>audio</B> track you invoke unsigned 8 bit encoding so you'll probably
  87 never use it.<P>
  88
  89 When you specify RAW for a <B>video</B> track you get RGB packed
  90 frames.  RAW video supports alpha channels.  To get RGBA packed frames
  91 you can then issue <P>
  92
  93 <CODE>
  94 int quicktime_set_depth(quicktime_t *file, int depth, int track);
  95 </CODE><P>
  96
  97 specifying a depth of 32.<P>
  98
  99 <H1>TWOS</H1>
 100
 101 Twos is the preferred encoding for uncompressed audio.  It stores 8,
 102 16, and 24 bit audio, interleaved for multiple channels.  The 8 bit
 103 mode is signed.  The 16 and 24 bit modes are big endian signed.
 104
 105 <H1>Vorbis</H1>
 106
 107 This is the preferred encoding for compressed audio although it
 108 probably won't be supported by Microsoft or Apple any time soon.  It
 109 takes the following parameters:<P>
 110
 111 <CODE>
 112 vorbis_bitrate (int)<BR>
 113 vorbis_max_bitrate (int)<BR>
 114 vorbis_min_bitrate (int)<BR>
 115 </CODE><P>
 116
 117 Units are bits per second.