Question

We know F4F is Adobe’s fragmented MP4 file format for HTTP Dynamic Streaming. A tool called F4F Packager could convert an F4V file to several F4F files and a manifest file(F4M).

My question is, how to convert such F4F files back to an F4V or MP4 file?

Answer 1

We finally found a simple method to merge & convert .f4f files -> .flv file, in which only ‘mdat’ box is usefull. Here is a the php code:

<?php
  function ReadInt24($str, $pos)
    {
      return intval(bin2hex(substr($str, $pos, 3)), 16);
    }

  function ReadInt32($str, $pos)
    {
      return unpack("N", substr($str, $pos, 4))[1];
    }

  echo "\nKSV Adobe HDS Downloader\n\n";
  $flvHeader        = hex2bin("464c5601050000000900000000");
  $firstVideoPacket = true;
  $prevTagSize      = 4;
  $fragCount        = 0;

  isset($argv[1]) ? $baseFilename = $argv[1] : $baseFilename = "";
  $baseFilename ? $outputFile = "$baseFilename.flv" : $outputFile = "Joined.flv";
  while (true)
    {
      if (file_exists("$baseFilename" . $fragCount + 1 . ".f4f"))
          $fragCount++;
      else
          break;
    }
  echo "Found $fragCount fragments\n";
  $flv = fopen("$outputFile", "wb");
  fwrite($flv, $flvHeader, 13);

  for ($i = 1; $i <= $fragCount; $i++)
    {
      $frag = file_get_contents("$baseFilename$i.f4f");
      preg_match('/(.{4})mdat[\x08\x09\x12]/i', $frag, $mdat, PREG_OFFSET_CAPTURE);
      $fragLen = ReadInt32($mdat[1][0], 0) - 8;
      $frag    = substr($frag, $mdat[1][1] + 8, $fragLen);
      $pos     = 0;
      while ($pos < $fragLen)
        {
          $packetType  = $frag[$pos];
          $packetSize  = ReadInt24($frag, $pos + 1);
          $packetTS    = ReadInt24($frag, $pos + 4);
          $totalTagLen = 11 + $packetSize + $prevTagSize;
          if (($packetType == "\x08" && $packetSize > 4) or ($packetType == "\x09" && $packetSize > 40) or ($packetType == "\x09" && $firstVideoPacket))
            {
              if ($packetType == "\x09" && $firstVideoPacket)
                  $firstVideoPacket = false;
              fwrite($flv, substr($frag, $pos, $totalTagLen), $totalTagLen);
            }
          $pos += $totalTagLen;
        }
    }

  fclose($flv);
  echo "Finished\n";
?>