The PowerPoint® Blog

Not all streaming media is created equal. The most advanced streaming media formats are a two-part strategy; first the streaming media is created in multiple versions, second it uses a special streaming media server.

The advantage of multiple bandwidth media is that a viewer with a slow connection gets a lower-quality movie. A viewer with a high speed connection gets a higher quality, larger bandwidth movie. The simple explanation is the movie has several versions all contained in a single file. The streaming media server has the ability to determine the speed of the connection of the viewer and shows them the file that is optimum for their connection.

A Streaming Server is designed specifically for streaming media. It runs specialized software that allows it to “see” the viewer’s connection speed, work through most firewalls, handle large simultaneous connections, implement DRM (Digital Rights Management) and stream without downloading. The last point is the “magic”, it literally plays the streaming media directly from server not the (progressive) downloaded file.

A (standard) Web server is not designed for streaming media, but it is the most common server and tons of streaming media is hosted on it. It streams using a method called progressive downloading. The file is downloaded to the computer’s browser cache and can only play what has been downloaded. Seeking, or jumping, ahead does not work until the entire file is downloaded. Playback is also more likely to be interrupted by periods of buffering (when the player is not receiving the file fast enough) and playback can be affected by the number of people trying to view it at the same time.

Note: A multiple bandwidth file can be hosted on a web server, but because a web server cannot recognize the various speeds built into the file it simply plays the highest bandwidth option (which is most likley poor playback quality as most viewers will not be able to support the super high bandwidth version). It’s like putting a square peg in a round hole – a bad idea…

– Troy @ TLC

In the Bandwidth Math posts, the formulas figured how a movie would play if it was just sent directly to the computer playing in real-time. To play a movie of any decent size and audio quality you would need a pretty fast connection. Fortunately we have ways to get around that!

1. Buffer a portion of the movie before playback begins with a PreLoader. People are patient for a short time. So without stretching that patience, let their computer buffer a portion of the movie, so as it plays, the next sections download. This could allow a high bandwidth movie, that according to the formula would need a 1.1 Mbps connection, to play smoothly on a 768 Kbps connection – because even though it is not downloading fast enough for the connection, we gave it a head start which allows it to outrun the viewer’s connection speed.

Most software makes this very easy. Here is Camtasia’s Preloader options:

2. Self-Paced Presentations have a built-in PreLoader effect. When the presentation pauses between slides, the person is busy reading the content on the slide AND their computer is busy downloading even more of the movie!

3. Break into a series of smaller linked movies. The smaller the file size (even if it has a large playback area) the faster it will play. So if the 20 minute presentation with 10 slides at 320×240 is a 50 MB file, it is geared towards High Bandwidth viewers. But if it is broken into 10 (seamlessly) linked movies that are roughly 2 MB each, now the same movie and playback size is viewable by much lower bandwidth connections.

4. Lower the Audio quality. If your presentation has music in the background, it does not need to be high fidelity stereo quality. Same goes for sound effects and speaker narrations. This will make the file size smaller. Encode it as:
– Mono vs Stereo.
– .MP3 vs .Wav
– 8 bit vs 16 or 24 bit
– 22,050 or 44,100 Hz vs 96,000 Hz

These are just a few tips. Look through all of the options offered with the software you are using to develop the streaming media and take the time to experiment with them by creating multiple versions.

– Troy @ TLC

A movie is a series of images played rapidly to create movement. Remember webcasts are all about throwing away unneeded data. The Key Frame is a critical component in what the file size will be.

Video software takes the original movie and compresses it. The Key Frame compression process only keeps the changes from one frame to another. So if you have a PowerPoint slide on Frame 1 and the only difference in Frame 2 is the mouse moves, Frame 2 will only consist of the part that shows the mouse movement.

With compression there are two types of frames:
1. Key Frame: the entire frame
2. Delta Frame: only has the area that changed

Key Frames
Within video software is the option to change the Key Frame Rate. The fewer Key Frames you use the smaller the file size. Here are two examples:
1. For PowerPoint content, where little changes from frame-to-frame, use a high Key Frame Rate (10-80).
2. For live video, where the constant motion has lots of change from frame-to-frame, use a low Key Frame Rate (1-12).

Frames Per Second and Key Frame Rate
Within video software the Frames Per Second (fps) can be adjusted. We need to consider the fps when setting the Key Frame Rate. We need to really consider how much changes from frame-to-frame how often. Here are to examples:
1. If encoding at 30 fps and the Key Frame Rate is 80, a new Key Frame will occur very quick – about every 2.5 seconds.
2. If encoding at 5 fps and the Key Frame Rate is still set at 80, the Key Frames are nearly 40 seconds apart.

– Troy @ TLC