flash FMS的一些最优参数设置

原文地址

对任何使用影音串流的 FlashCom 程式来说，影音串流的品质是极重要的，但调校相关参数却需要非常好的技巧及多次测试，无意间逛到国外有人已写好一个计算建议值的小程式，应该对参数的决定有很大帮助。

参数的设定可能因以下因素而不同 ( 并非只看这些因素 )：

使用者连线至主机的频宽，是使用 ADSL、一般的区域网路还是无线网路？
有多少人广播串流？愈多人广播串流，影音品质应调得愈低，以控制总流量。
在相同的频宽下，我们可以提供较低品质但关键影格多的影像 ( fast images ) 或较高品质但关键影格少的影像 ( slow images )，或提供精细品质但更少关键影格的影像 ( high quality )。如果每个使用者都是透过区域网路来连接 FlashCom 主机，那我们就可提供精细品质且关键影格又多的影像 ( high bandwidth )。
影像长宽比，1 / 1 ( portrait )、6 / 5 ( normal )、9 / 5 ( landscape )。
要调整参数我们必需在 client 端的 ActionScript 中使用下列方法：

Camera.setQuality
Camera.setKeyframeInterval
Camera.setMode
Microphone.setRate
具体算法：

m_pb.addEventListener("click", _root);
_root.click = function() {
  var bwLabel = m_bw.value;
  var numUsers = m_numUsers.value;
  var ratio = m_ratio.value;
  var speed = m_speed.value;
  trace(bwLabel+", "+numUsers+", "+ratio+", "+speed);
  //Mic rate
  var theRate = 0;
  var bwDown = 0;
  var bwUp = 0;
  switch (bwLabel) {
    case "modem":
     theRate = 5;
     bwDown = 40;
     bwUp = 28;
     break;
    case "dsl":
     theRate = 11;
     bwDown = 300;
     bwUp = 100;
     break;
    case "lan":
     theRate = (numUsers < 2) ? 22 : 11;
     bwDown = 600;
     bwUp = 300;
     break;
   }
  m_setRate_txt.text = "mic.setRate("+theRate+");";
  //Video values
  var FPSsum;
  var FPSlim;
  switch (bwLabel) {
    case "modem":
     FPSsum = 3;
     FPSlim = 2;
     break;
    case "dsl":
     FPSsum = 24;
     FPSlim = 12;
     break;
    case "lan":
     FPSsum = 50;
     FPSlim = 15;
     break;
   }
  // BWsum is = 2/3 * down
  var BWsum = (2/3) * bwDown;
  // BWlim is = up/2
  // except LAN which is 150
  var BWlim = bwUp;
  if (bwLabel == "lan")
   BWlim = bwUp/2;
  // bw is = min(BWlim, BWsum/numUsers);
  var bw = Math.min(BWlim, BWsum/numUsers)*1024/8;
  var w;
  var h;
  switch (ratio) {
    default:
    case "portrait":
     w = 120;
     h = 120;
     break;
    case "normal":
     w = 140;
     h = 104;
     break;
    case "landscape":
     w = 160;
     h = 88;
     break;
   }
  // fps is = min(FPSlim, FPSsum/numUsers);
  var fps = Math.min(FPSlim, FPSsum/numUsers);
  // keyFrameInteval is = max(2*fps, 4)
  var kfInt = Math.max(2*fps,4);
  //if (broadband and lan) set to 300 (total up)
  if ((speed == "high bandwidth")&&(bwLabel == "lan"))
   bw = bwUp*1024/8;
  m_setQuality_txt.text = "cam.setQuality("+Math.round(bw)+", 0);";
  m_setKeyframeInterval_txt.text = "cam.setKeyframeInterval("+kfInt+");";
  switch (speed) {
    case "slow images":
     m_setMode_txt.text = "cam.setMode("+w+", "+h+", "+Math.min(1,fps)+");";
     break;
    case "fast images":
     m_setMode_txt.text = "cam.setMode("+w+", "+h+", "+fps+");";
     break;
    case "high quality":
     //  w = 2*w
     //  h = 2*h
     //  fps = fps/2
     m_setMode_txt.text = "cam.setMode("+w*2+", "+h*2+", "+fps/2+");";
     break;
    case "high bandwidth":
     m_setMode_txt.text = "cam.setMode("+w*2+", "+h*2+", "+((bwLabel == "lan") ? fps : fps/2)+");";
     break;
   }
}
_root.click();