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JPG, GIF, PNG or SVG
There are four types of images that can be used on web pages: GIF, JPG, PNG, and SVG.
Use GIF files for images that have a small, fixed number of colors. GIF files are always reduced to no more than 256 unique colors. The compression algorithm for GIF files is less complex than for JPG files, but when used on flat color images and text it produces very small file sizes.
The GIF format is not suitable for photographic images or images with gradient colors. Because the GIF format has a limited number of colors, gradients and photographs will end up with banding and pixelation when saved as a GIF file.
Use JPG images for photographs and other images that have millions of colors. It uses a complex compression algorithm that allows you to create smaller graphics by losing some of the quality of the image. This is called a "lossy" compression because some of the image information is lost when the image is compressed.
The JPG format is not suited to images with text, large blocks of solid color, and simple shapes with crisp edges. This is because when the image is compressed the text, color, or lines may blur resulting in an image that is not as sharp as it would be saved in another format.
The PNG format was developed as a replacement for the GIF format when it appeared that GIF images would be subject to a royalty fee. PNG graphics have a better compression rate than GIF images which result in smaller images than the same file saved as a GIF. PNG files offer alpha transparency as well as animation.
PNG images, like GIFs, are not well suited to photographs. It is possible to get around the banding issue that affects photographs saved as GIF files using true colors, but this can result in very large images. PNG images are also not well supported on older cell phones and feature phones.
SVG images work well for non-photographic information, in that they can be scaled in size well.
Media encoding options
See also: Wikipedia: YouTube #Quality and formats
Between 3gpp, flv, mp4, and webm, it appears that mp4 may be the best all other things being equal.
However, WebM is better for streaming and slightly smaller file size. MP4 will play on more devices, as well as on Windows (outside of browser). Quality of MP4 may be slightly better.
Movie DVD structure
Commercial DVD movies are encoded using a combination MPEG-2 compressed video and audio of varying formats.
When you insert a video DVD into your computer, you can open the DVD and view the contents just like a folder on your hard drive. Most video DVDs have two folders in the root directory – AUDIO_TS and VIDEO_TS. These names are short for "audio transport stream" and "video transport stream."
The AUDIO_TS folder is used for storing audio data for DVD-audio discs. If the DVD contains only video content, the AUDIO_TS folder will be empty. Therefore, most DVDs have an empty AUDIO_TS folder.
The VIDEO_TS folder contains all the DVD's video data and playback information.
The .VOB (video object) files contain the majority of the DVD data. This includes the actual video and audio data as well as subtitles, additional viewing angles, and other video-related data. They can be a maximum of 1 GB in size, which is why multiple .VOB files are often required when creating a video DVD. Some programs can extract video data from .VOB files or play back the video data directly.
The .IFO (information) files contain basic information about the DVD and the corresponding .VOB files. This includes what data should be loaded when the DVD is first inserted, where the DVD chapter markers are located, and what DVD commands can be entered by the user.
The .BUP (backup) files are exact copies of the .IFO files. The serve as backups in case the original .IFO files become corrupted and cannot be read. Since the DVD cannot be played back without valid information files, the .BUP files reduce the risk of a small error or scratch on the disc ruining the DVD.