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Saturday, August 02, 2008
Video Compression Workshop – Helpful Advice
Stereo, or No?
Most professional videos have two (or more) channels of audio. This can cause unnecessarily large file sizes and playback problems for viewers who listen on mono speakers. While you’re attracted to Stereo, give Mono some serious thought.
• Stereo Dialog could result in many users not being able to hear the audio through their built-in speaker. Always pan dialog tracks to center before making your self-contained or reference clip to encode.
• Stereo data is twice the size of mono data. Get the size down.
• Unless you’ve got some dramatic environmental effects or music going on, Stereo is just overkill for the personal computer environment.
• If you really want stereo, look at your format of choice to see if it supports Joint Stereo. This will only save separate data for each speaker when there is a difference between the left and right channels. This can save a lot of space.
Flicker Fix
If you shot your video using a traditional standard def camera, you likely have interlaced video. On a Television this produces smoother motion, on a computer it produces junk. You’ve got two approaches to take
1 If the video is being acquired solely for web or theatrical you can shoot Progressive (such as 24P, 25P, or 30P). If your client likes the look, they may want to shoot 24P anyways.
2 Apply a de-interlace filter to your clip to all video shot with interlacing. If you are going to be producing several compressed formats, you may want to pre-process the source sequence by adding a de-interlace filter in your NLE. If you have the option, you may need to specify which field to use. For digital formats, both NTSC and PAL, you should choose lower field first.
Get the Wash-Out
One common client complaint is that the video often looks washed out on their computers. This is because video and computers operate in different color spaces (YUV vs. RGB). Video signals operate between an RGB value of 16 thru 235. Computers use an RGB value of 0 thru 255. You will need to restore the black and white point of your image. Look for an option called Black Restore and White Restore. To fine tune this effect, you will need to experiment with the amount and smoothness settings. Be sure to invoke your preview window to see the results before encoding with the settings.
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Hello
I have i mp4 video with screensize 640*480 that i have to adjust to screensize 320*180.
How do i do that ?
Posted by on 10/04 at 01:32 AM
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