Streaming Video: An Overview
Frame Size
Another major factor to consider is the physical size of the video. The larger the video is on screen the greater the demand is places on bandwidth. Common video sizes are:
- NTSC : 640 by 48
- PAL (The European Standard ): 768 by 576
- Wide Screen: 720 by 576
- Flash Video: Pick a number
Obviously creating an FLV at 720 x 576 is going to pose a huge issue to the poor viewer. This is why most Flash Video uses 320 by 240, 240 x 180, 160 x120 and 80 x 60. Even so, if you keep the user, not the technology, foremost in your mind, the astute developer creates the video by targeting the bandwidth.
A larger video- 320 by 240- requires more screen real estate. It will also have a higher resolution and better
quality. The downside is a larger file size and a rather large appetite for bandwidth making it difficult, at
best, for the poor user with a dial up connection.
A smaller video 240 by 180 or 160 x 120, on the other hand has a smaller browser footprint and the trade off
will be a decrease in resolution and detail. The upside, of course, is a smaller file size and a reduced
bandwidth requirement.
Regardless of whether you use Flash Professional 8, Flix Pro or Sorenson Squeeze 4.3 to create the video they are all going to ask you the following questions:
• What bit rate will be used to stream the video?
• What frame size will be used to present the video?
• What frame interval should be used for the key frames?
To help you answer those questions here is chart that gives you some suggested values:
If you are targeting a 56K modem you must keep the rate under 40K and don’t use less than
16 K for the audio. The keyframe number is an approximation. Start there and work backwards.
Note: These charts are adapted from an encoding article prepared by William Caulfield at the Macromedia Dev Center. Another great resource is Robert Reinhardt's Bit Rate Calculator on the Adobe site.
This work is licensed under a Creative Commons License.
