A few days ago, I was asked to write up something about video quality and conversion speed. There are a lot of ideasfloating around the web on this topic, written by people who think they know a lot about video (including me).  In most of these write-ups, people just throw around a bunch of numbers, based on device specifications or from information read somewhere else. Because some of this information is spread around so much in different locations, many people believe this information to be facts. 50 people saying the same thing can’t be wrong, right? Well, if they all use the same source, and never actually tested it for themselves, who knows if it actually is.
So to clear some things up, I am writing this article.

This information is not specific to DVD Catalyst. it can be applied to anything related to video conversion.

What is video.

Video is basically sequence of images (frames) displayed in succession. The individual images are slightly different from each other, and depending on the speed of playback of the sequence (frame-rate) the “movement” of the video is smooth or slide-show style.
Movies, TV Shows, Cartoons are in all essence the same, just a bunch of images displayed in succession. The speed of which the individual images change is usually between 25 and 30 changes per second, based on the limitation of the human eye.
The quality of the video is determined by the quality of the individual frames of the video. The better the individual picture looks, the better the video quality is, BUT unlike looking at an actual picture, video switches these images so fast, that small inconsistencies are barely noticable.

Video Codec.

Without explaining this in full detail, a codec is simply put a method to make something smaller, and make it bigger when needed.  An hour of music on a music cd takes bout about 650MB, but if we compress this to (codec) MP3, we end up with the same hour of music at a file-size of about 150-200MB (3x smaller, depending on the quality setting used) A picture from a professional digital camera could take up to 40MB in size, but to be able to send it by email, it usually gets compressed using the JPEG codec, which could reduce the file size to 1MB for example. If we take a huge Word document, with pictures and stuff, we can compress it to a ZIP file to make it a lot smaller as well. A video codec works the same way. It “encodes” (compresses) the individual pictures of the video using some compression system, and to play the file later on, the video player “decodes” (decompresses) the video so you can see it.

There are a lot of different video codecs, all with their own purposes.

MPEG1/2, used for LaserDisc, VideoCD and DVD
DIVX/XVID, used for some types of internet-video, often used for sharing video
3GP, used for older video on camera phones.
WMV, FLV, for internet streaming.
H264, used on BluRay, Apple’s iTunes and HD-DVD

Some codecs are better for quality (H264), while others are better for low performance requirements (3GP, MPEG1/2).

H264 AVC

H264 is currently the most popular video codec on the market. It is used in most devices currently available.
The main difference between H264 and other formats such as DIVX and XVID is that it is capable of making video a lot smaller than these, while maintaining a great quality. Because of this, H264 is used for Bluray movies, YouTube HD, and even the movies and TV shows you can rent/purchase from iTunes. If you would use one of the other formats for this, the file would either not look as good, or the file would be a couple times bigger in size.
However, because of the better compression, it takes a lot of computer power to handle video using this format. For conversion as well as playback, your computer needs to do a lot of work. While a great looking XVID video file will play fine on a netbook, playing a H264 video file of the same quality on the same netbook, you will notice it will stutter/freeze all the time, due to the lack of processing power. As a result, conversion to this format will be considerably slower than converting to an other video format. For devices that can play format, such as the Droid, iPod/iPhone, PSP, recent HTC and Blackberry models for example, hardware support is build-in that handles the video decoding instead of the processor.

Video quality:

Unlike Zip-files, video compression is not loss-less, which means that you will lose some of the quality. Depending on the quality (bitrate) setting used, it will be a little or a lot. As mentioned earlier, video is a sequence of pictures, and the quality of the individual picture affects the overall quality of the video. The compression is determined by the size of the pixture (width and height) and the color depth (16bits, 32bits) and what compression codec is used.
For uncompressed video, each individual frame will take up a filespace that is calculated by the following:
picture width x pixture height (amount of individual pixels) x depth (16 bits per pixel, 32bits per pixel)
For the sequence, multiply this by the amount of picture changes per second (framerate), and you end up with a bits per second value (bps/kbps etc).
The Video Codec, depending on which one is used, will reduce this value.
The quality of video is relative. Everyone’s perception of quality is different. Many people on the web, posts on forums etc, suggest to use the maximum the device can handle. While the video will look perfect, there is a price for all that quality; The conversion time is slower and the resulting file is bigger. While having video at the best possible quality is great to show off what your device can do, but when you are on a trip, and only managed to fit a few movies on your device in this quality, it might be more desirable to have them a little less than perfect so you have 2x as many with you.
You are already making a compromise bny watching the video on a smaller screen, and in all honesty, most people don’t even notice a small quality difference.
Here is a small test in regards of audio. While not directly related, it clears some things up.
http://www.noiseaddicts.com/2009/03/mp3-sound-quality-test-128-320/

To sum things up, don’t just take someone’s word for what quality settings you should use. Play around with some different settings, and save yourself some cash by not having to pick up another memorycard. The choice is yours.