Streaming Video: An Overview
Optimizing video for web delivery
Now that you understand how your video gets from there to here and the dangers you face here are some tips from Adobe in preparing video for web streaming
- Crop your video:
Removing 5% from the edges of the video- 100 x 100 cropped down to 95 x 95 gets rid of the edge artifacts. Obviously those numbers are not appropriate for video but it does get rid of any tearing or black edges around the frame edges. When you do crop pay very close attention to the 4:3 aspect ratio. Another thing to keep in mind is that the dimensions of the video should also be in multiples of four. This is because compression calculations divide each frame image into blocks of four or 16 pixels. By keeping to the multiples you are assured the aspect ratio won’t change.
- Image size:
If broadband is in your target no higher than 320 x 240 or 240 by 180. If dial up figures into the mix, 160 by 120 is the max.
- DeInterlacing :
Your TV shows the picture in alternating rows using the interlacing process. Computer monitors don’t work this
way so be sure to deinterlace any video in Premiere, Final Cut Pro or After Effects. You can’t deinterlace video
using the Flash Video Encoder.
Brightness,contrast, hue and saturation: Do this adjustment in a video editing application. Don’t use a Flash
filter. Using Flash for this purpose will simply eat up processor power and bandwidth.
- Gamma correction:
Gamma is the mid tone and adjusting this before compressing for the web helps create more whites without brightening the entire range of pixels. In many respects, if you use Levels in Photoshop to adjust images, the middle slider is the gamma slider. Same concept in video editing software.
- Black and White points:
The other two sliders in the Levels dialog box set the color to be used for the black and for the white. Any
color value beyond that point is shifted to black or white and all the other color values in the image are
readjusted. This is a great way of reducing noise- those almost black pixels- in the flat black area of the
screen.
Remove noise from the audio: Export the audio track to an audio editor such as Audition to remove any extra
noise in the audio track. In web video, noise is usually amplified resulting in an unintelligible sound track.
- Mono is good :
Stereo is OK but doubling the bandwidth requirement to produce an extra audio track simply doesn’t make sense. Save the stereo sound for your CD or DVD.
- Skip the fancy stuff:
Complex transitions need bandwidth. Use straight cuts and focus on the content not the effects.
- Make titles longer, simpler and let them linger:
Think of trying to get the Star Wars titling sequence into a 160 by 120 space and you get the idea.
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