There are several out of date threads like this. I think I might post this as a general topic for people to refer to. (Note: This gets buggy if you are using a v-cam)
There are several (good) ways of doing this but this is by far the safest (you don't have to buy any sketchy programs) and most efficient method I've found to get the best quality Flash to Youtube transfer. The reason for this is that pretty much all video capture software will drop or add frames. Or won't read actionscript or symbols properly.
1. Download the Kurst SWF Renderer flash extension HERE Install it into Adobe AIR.
2. Restart Flash. Export your SWF.
3. Convert your SWF into a PNG sequence (make sure all the settings are correct).
You can carry on from here in several ways.
4a. If you have AfterEffects, import the PNG sequence. you can use AfterEffects to export in any video format you like.
4b. If you don't have AE, then re-import the PNG sequence into a new Flash Document. Now that you don't have any more symbols to deal with, the exported video should come out just fine.
5a. If your soundtrack is simple, then you can just re-sync them into the project in whichever program you're using.
5b. If it's very complex, then the best thing to do would be to create a new .fla and copy all the frames with sound at the same time from your original .fla (so that they stay in order and the whole thing is the same length as the project) into the new .fla. Then, export the new .fla as a very high quality audio file. That will give you an audio file you can re-import into flash and stick next to your video. The audio file should exist even where there is no sound.
Video Compression: There is no agreed upon method about this. I usually export as .F4V or .FLV depending on how big the file is. Here is a good starting point.
H.264 video codec set to 2000Kbits/sec (2Mbits/sec or 250KBytes/sec)
320×240 video size (deinterlaced or simply use one field)
Audio Compression: Mono audio with AAC codec at 64 Kbit/sec (or 128 Kbit/sec for stereo)
Best Encoding Quality
Let me know if you can work it this way, so I can figure out how to put it when I make a thread.