Divx Compression

[RustyBob]

Just a question regarding the reason for compression. My thought was to compress video and store on a hard drive, and view it later on a 50" plasma screen. Is this feasible ? The more I read it becomes clear, or semi clear, that the purpose for compression is for ipads, ipods, smart phones, game boxes and the like. Or peer to peer transmission.

[guns1inger]

Pretty much any video you watch is compressed. From DVD to Bluray to digital broadcast material, it is compressed to often a very large degree. Uncompressed video requires large amounts of space and resources to manage. The question is really what is the best type of compression, and how much should be applied. Divx, for example, offers two different types of compression. The older style Divx compression uses mpeg-4 part 2 (the same as xvid), but it also now offers the superior mpeg-4 part 10 compression (aka AVC or H264) in the MKV container. This is closer to the compression used in Bluray and a lot of online content. However even Bluray, when compared the the uncompressed 1080p source, is very heavily compressed.

Storage is another issue. Where it was once a premium, now it is a commodity item that is relatively cheap and simple to add. Run out of space - go buy another TB or two of e-sata or USB disc and plug it in. This means that the level of compression required is no longer as great (the days of having to squeeze a movie into a CD sized 70MB are gone except for the die-hard downloaders), and range of players now available allow for a wider range of compression types to be used. It is now at the point where many are no longer squeezing DVDs down for storage, but are ripping whole discs to ISO format and keeping them without further compression.

H.264 is currently the compression de jour, and provides a good trade off between quality and size. I have been compressing DVDs using H.264, and have found an acceptable size is between 1.5 and 2 GB (depending on the running time), including the original AC3 audio where possible, and a width of 704 pixels. Another alternative is to use quality based encoding and not worry about file size at all.

Ultimately, you have to accept some compression for practical reasons (if for not other reason than nothing but your OPC can play back uncompressed video). You have to look at your source, your available storage and your tolerance for quality levels, and make a call on what is right for you. This may mean experimenting with different levels of compression, with fixed bitrates versus quality based encoding, until you find what works for you.