if i´m not mistaken, that´s a pretty big video clip, so every now and then your CPU slows down, and upps, sh*t happens. the other thing is that your video is in MPEG format so is very compressed and flash works better with .MOV and .AVI formats. Try to use Sorenson Squeeze.
I find it helps to keep all the framerates in syc as well, so if your imported movie is at 30 fps it will help to run your .swf at the same rate, or half rate (15) and use the sync to Flash frame rate in the import settings.
Please be aware that Flash MX has had many reported problems with audio sync. The best way around these problems is to import your video at a one to one framerate as the source and to use a quality setting lower than 100%. You can also try using a 3rd party software, like our Flix encoder which offers excellent sync.
Here are other reasons why you may be losing audio sync:
To start it may be helpful to explain a couple of things:
A) Flash video has two framerates: 1) a video framerate, which is the number of distinct video frames per second in your video, and 2) a SWF framerate, which is the number of SWF frames in your final Flash video. These are not the same thing and you have to keep track of both - and how they relate to each other and to the source video framerate. Flash video is different in this way then standard video which has only a single video framerate.
B) A factor is a mathematical term that describes one of two or more quantities that divides a given quantity without a remainder. For example 1, 2, 3 and 6 are factors of 6; 1, 2, 3, 5, 6, 10, 15, and 30 are factors of 30, and so on. Potential reasons for loss of audio sync:
-The video framerate of your output SWF conflicts with the video framerate of your source video. The video framerate of your SWF video should be a factor of your source video framerate.
-The SWF framerate of your output SWF conflicts with the video framerate. The SWF framerate of your SWF video should be equal to or a multiple of your video framerate.
-The video SWF file created uses up too much RAM for the system it is running on, resulting in a loss of sync.
-The SWF file that the video is embedded (or loaded) in uses up too much processor power for the system it is running on, resulting in a loss of sync.
-The source has errors, which cause loss of sync.
-The source codec used is not 100% supported.
-The computer used to encode lacks the processing power and/or ram required to encode with sync.
-There may be a conflict between the audio settings you are using (frequency and bitrate) and the audio settings of your source video. You can try to experiment by altering your settings to see if it helps the problem. Often, increasing the frequency and bitrate can solve this problem.
-The video framerate being used is very low and the resulting video appears to have audio and video out of sync (especially with talking mouths) but in fact it is in sync and the appearance of sync loss is caused by the very low frame rate.
-The audio and video of the source video was captured with separate cards which results in a loss of sync that gets worse with subsequent generations. We recommend using a capture card with both audio and video inputs to help keep the video and audio in sync. We use an Osprey capture card with audio and video inputs. Though the Osprey card is less than many other cards, we have found the quality to be superior.