A Flash Player movie plays smoothly if the Flash Player is able to receive data over the network connection at about the same rate that the movie is set to play in frames per second.

To ensure that your Flash Player movie plays smoothly from start to finish:

	Make sure the size of the data required to display each frame is as small as possible.
	Make sure the size of the data required to display a series of frames takes no longer to download than it takes to play the series of frames.

To play any frame, Flash requires all elements of the frame, such as event sounds, bitmaps, and vector shapes, to be downloaded in their entirety. If the movie reaches a frame that can't be rendered because the data requires more time to download than data in previous frames, playback of the movie stops until the data finishes downloading.

Therefore, if your movie has complex items or a large number of items in the first frame, it may take awhile to download all those items before the first frame can be displayed. If other frames are also large or complex, your movie may play in spurts slowing down to wait for data and then speeding up when it has enough data to play the frames faster.

Optimizing sound
Sound is data intensive. The quality of the sound output and the length of playback factor prominently into the amount of data required. Sounds with higher sample rates (22.5Khz and above) retain a greater degree of quality, but almost always require too much data to realistically stream sound to the Flash player over a 28.8Kbps modem. Flash utilizes compression to help reduce the size of the data - but even the maximum compression allowed in Flash might not be sufficient to deliver high quality audio over longer periods of play. Here are some tips to use sound more efficiently.

Use the lowest bit-depth and sample rate acceptable to achieve the smallest data size
Sound quality deteriorates as the sample rate declines, so you may find lower sample rates yield a more even playback but also poorer quality audio. Try to find a happy medium between quality and data size.

Keep sounds short
Flash doesn't have the same type of compression capabilities as Shockwave Streaming Audio, so it is ill suited as a means to deliver longer audio programs. Loop smaller sounds to achieve longer audio playback. Smaller amounts of sound data are downloaded once and used repeatedly.

Use preloading techniques to trim down the amount of data needed per frame or per second
Watch the size report closely for clogging of data near keyframes. Choose the sound synch option that offers best performance for each sound you use. Remember, data for sound synched to events are delivered all at once when needed for playback; stream synch delivers the sound data over the specified series of frames.