thecoalman - 4:00 pm on Dec 27, 2008 (gmt 0)

I'm not familiar with flash video but the same principals apply for any type of video. I'd venture to guess you don't have enough bitrate or the player scales video poorly.

The first thing to understand is how compressed video is created. If for example you start out with format that is only lightly compressed like DV-AVI each frame of video has an individual picture which is lightly compressed. To achieve more compression with codecs like MPEG, WMV etc. Frames are put into what is called a group of pictures (GOP). The first frame of a GOP is called the I-Frame and that is the only one that is full frame, subsequent frames are made up of previous frames. This why you'll see a lot of macroblocking during fast motion on some clips that will look normal when no one is moving. There's not enough bitrate to store all these changes from frame to frame so you get big blocks or macroblocking as it is commonly referred to.

The bitrate required for a given video so these blocks don't occur varies depending on the resolution of the video, the codec used and the content of the video. I'll use MPEG2 as example which is used for DVD. if you use a resolution of 720X480 you can set a bitrate of 8000kbps which should eliminate all but minute macroblocking, anything over 8000kbps and you're just creating a larger file. Once you get down around 4000kbps you'll start to get some real bad macroblocking and at the point you're better off using a lower resolution. You'll lose detail BUT you won't have all those blocks.

Assuming the player scales video well a 320X240 MPEG video encoded at 1000kbps will be superior to a 720X480 video encoded at 2000-3000kbps especially if there is large amount of action in the video.

So the short answer is you need more bitrate or a lower resolution but that's assuming you're encoding from a good source video to start with. You can't take a stepped on video and reencode it to higher bitrate to make it look better. A video should be encoded to compressed format from the highest quality source you have once and only once. Each recompression will degrade the video, how much "depends".

Codecs like WMV or others made for higher compression can use much lower bitrates than the examples I provided.