取得 FLV 內的 header 資料

依據 osFlash 裡 FLV 檔案資料格式的說明, 利用 Flash 開發「取得 FLV 檔頭資料及串流資料」的 AIR app。
要注意的是 meta 裡包含兩個 AMF packets, 所以需使用 ByteArray.readObject() 兩次。
Flash frame AS3:

import flash.filesystem.File;
import flash.filesystem.FileMode;
import flash.filesystem.FileStream;

var file:File;
var fs:FileStream;
var flvFilter:FileFilter = new FileFilter("Flash Video", "*.flv");
var header_ba:ByteArray;
var stream_ba:ByteArray;

function bClick(e:MouseEvent):void {
 var targetName:String = e.target.name;
 switch (targetName) {
  case "open_btn" :
   file = new File();
   file.browseForOpen("Open", [flvFilter]);
   file.addEventListener(Event.SELECT, readFLVHeader);
   break;
  case "show_btn" :
   readStreamHeader();
   break;
  case "close_btn" :
   fs.close();
   break;
 }
}
open_btn.addEventListener(MouseEvent.CLICK, bClick);
show_btn.addEventListener(MouseEvent.CLICK, bClick);
close_btn.addEventListener(MouseEvent.CLICK, bClick);


function readFLVHeader(e:Event) {
 filename_txt.text = file.nativePath;
 fs = new FileStream();
 fs.open(file, FileMode.READ);

 // read FLV Header
 header_ba = new ByteArray();
 fs.readBytes(header_ba, 0, 9);
 main_txt.text = "Signature: "+ header_ba.readMultiByte(3, "") +"\n";
 main_txt.appendText("Version: "+ header_ba.readUnsignedByte()+"\n");
 main_txt.appendText("Flags: "+ header_ba.readUnsignedByte()+"\n");
 main_txt.appendText("Offset: "+ header_ba.readUnsignedInt()+"\n");
 main_txt.appendText("---\n");
}
function readStreamHeader() {
 stream_ba = new ByteArray();
 fs.readBytes(stream_ba, 0, 15);

 main_txt.appendText("PreviousTagSize: "+ stream_ba.readInt()+" ----\n");
 var type:uint = stream_ba.readUnsignedByte();
 main_txt.appendText("Type: "+ type +"\n");
 // 取 3 bytes
 var bodyLength:uint = stream_ba.readUnsignedShort()<<8 | stream_ba.readUnsignedByte();
 main_txt.appendText("BodyLength: "+ bodyLength +"\n");
 var timestamp:uint = stream_ba.readUnsignedShort()<<8 | stream_ba.readUnsignedByte();
 main_txt.appendText("Timestamp: "+ timestamp +"\n");
 main_txt.appendText("Padding: "+ stream_ba.readUnsignedInt()+"\n");
 if (type == 0x12) {
  var t_ba:ByteArray = new ByteArray();
  fs.readBytes(t_ba, 0, bodyLength);
  // 設定 AMF 的格式, 即使是 on2 VP6 應該還是舊的
  t_ba.objectEncoding = ObjectEncoding.AMF0;
  // 第一個 AMF 物件是事件處理器的資料
  var obj:Object = t_ba.readObject();
  var str:String = QopDump.go( obj );
  main_txt.appendText("***\nEvent handler:"+str+"\n***\n");
  obj = t_ba.readObject();
  str = QopDump.go( obj );
  main_txt.appendText(str+"\n");
 } else {
  // skip the body
  fs.position += bodyLength;
 }
 main_txt.verticalScrollPosition = main_txt.maxVerticalScrollPosition;
}

FLV 的第一個 stream unit 應該都是 meta。較舊 FLV 的 meta 大多有問題, 沒有提供仔細而實用的資料。

較新格式的 FLV 其 Flags 通常是 13 而不是 5。


原始檔: parseFLV.fla
安裝檔: parseFLV.air