| 10 Feb 2007 03:21 am |
Wannabe Rep: 0 Joined: 24 Dec 2006 Posts: 63 OFFLINE | 1) What is video compression?
Way back in the day when digital video was first being born, video was stored in its pure, uncompressed format, much like digital audio (for those who don’t know, CDs were pure uncompressed digital audio data, while newer standards such as Dolby Digital, MiniDisc, and MP3 are compressed).
This meant that it took a LOT of space.
For comparison on how much space video takes over audio, no matter how its stored, take for example the FM radio spectrum.
TV Stations, like Radio stations, have a fixed frequency range which they operate on, however unlike FM we are never told the exact frequency at which they operate, our TVs are just hardwired with what frequency values correspond to channel 2, 3, 4 and so on.
| |
| | 10 Feb 2007 03:23 am |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | The ENTIRE FM spectrum exists in a tiny little gap between TV channels 4 and 5, which themselves (this is for a single channel) take something around 5 times more bandwidth than the whole FM band. Crazy, huh?
So one can imagine that back when digital video first came out, it was damn hard to store.
Nowadays we have 100GB RAID arrays being common in not-so-expensive consumer setups.
10 years ago, 10GB was an ENORMOUS amount of space!! Hard drives didn’t hold more than 500MB tops, but uncompressed digital video still took up the same space it does now.
This lead to people storing digital video to tape and doing things with it that way, but this made Non-Linear video-editing impossible.
| | | 10 Feb 2007 03:30 am |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | 
| | | 10 Feb 2007 03:32 am |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | Then along came video compression. Probably the earliest, and truly successful video codecs (CODEC stands for COmpressor/DECompressor) was MPEG1.
I’m sure you’ve all heard of MPEG (The Motion Picture Experts Group) in terms of its compression. But did you know that the actual standard for MPEG1 video is over a decade old?
Not only that, but the MPEG2 standard used in DVDs is more than half a decade old!
But how does compression work? Well like with any kind of compression there are two kinds: lossless and lossy.
| | | 10 Feb 2007 03:37 am |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | 2) Lossy Compression
This is the form of video compression most people are familiar with. 95% of all video codecs out there are lossy, meaning that when you compress the video and then decompress it, you do not get back what you put it.
Now, this isn’t as bad as it may sound. Obviously if you’re compressing something like a text document, you don’t want to lose any of the data, but with something like a picture, even if a few bits and pieces aren’t quite right, you can still make out the generally gist of the image.
Same thing with audio. Famous lossy codecs include MPEG1, MPEG2, MPEG4 (AKA DivX3.11, DivX4/5, XviD, Quicktime MPEG4), Wiindows Media Video, RealVideo, Sorenson, Indeo, and the classic Cinepak. — -and about the converting among MPEG1, MPEG2, MPEG4 (AKA DivX3.11, DivX4/5, XviD, Quicktime MPEG4) u can use Xilisoft Video Converter, which is a powerful, versatile video conversion software ,can convert video file between all popular video formats ,but the conversition is another problem, we can discuss next time
Last edited 10 Feb 2007 03:38 am by runningtiger | | | 10 Feb 2007 03:39 am |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | 3) Lossless Compression
Lossless compression, as the name implies, means that after compressing the video, and then decompressing it, you wind up with the exact same data as you put in.
This is comparable to something like ZIP or RAR (In fact, the most common lossless codec out there, Huffyuv, basically uses the same compression algorithm as ZIP on each frame of video to achieve its compression).
Lossless has the advantage that no matter how many times you compress it, you still haven’t lost any video data. The bad part is that most often you don’t save nearly as much space as you would with other lossy compression algorithms
| | | 07 Mar 2007 08:58 am |
Wannabe Rep: 0Joined: 13 Dec 2006 Posts: 57 OFFLINE | oh, that’s good
| | | 09 Mar 2007 09:52 pm |
Wannabe Rep: 0Joined: 13 Dec 2006 Posts: 57 OFFLINE | and can u say something about ripping ?
| | | 09 Mar 2007 09:56 pm |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | of course , ripping is the process of copying the audio and/or video data from one media form, such as Digital Versatile Disc (DVD) to a hard disk without the DVD copy protection screwing up your files
Almost every DVD disc is encrypted nowadays which prevents you from simply dragging and dropping its contents to your hard disk.
DVDs are encrypted by CSS, which scrambles the DVD file as it is copied.
| | | 09 Mar 2007 09:58 pm |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | There are several tools available which can easily bypass this problem simply by decrypting the DVD’s contents, such as DVD Decrypter, DVDFab Decrypter and Magic DVD Ripper , and if you want to convert the contents of the DVD¡¯s into other audio/video formats ,you can use Xilisoft DVD Ripper ,which is powerful, easy to use helping you rip DVD to AVI, MPEG, DivX, VCD, WMV, ASF, VOB, MP3, WMA , and other popular video and audio formats within a few clicks
| | | 09 Mar 2007 09:59 pm |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | In the mean time there are many settings you can customize, such as ripping DVD by custom file size, spliting output file to fit your CD-R, rip DVD any segment, select target subtitle and audio track, and so on.
While DVD Decrypter is a free tool that allows you to decrypt and copy DVDs to your PC’s hard disk.
From there you can watch them with the likes of WinDVD and PowerDVD, you can write them back to DVD-R / DVD-RW / DVD+R / DVD+RW / DVD+R DL / DVD-RAM media or you can convert them to VCD / SVCD / DivX for burning onto CD-R / CD-RW.
DVD Decrypter can write most types of CD / DVD images via its 'ISO Write' mode, and it supports all the latest writers (including booktype / bitsetting on many of the major ones - i.e. BenQ, LiteOn, NEC, Plextor, Sony). You can even use DVD Decrypter to erase / format your rewritable media!
| | | 09 Mar 2007 10:00 pm |
Wannabe Rep: 0Joined: 24 Dec 2006 Posts: 63 OFFLINE | So a ripper is a program that allows you to break this encryption and “rip” out the files from the DVD, without it being turned into garbage data. Basically, it allows you to copy files from the DVD to your hard-drive successfully.
The term “Ripping” comes from the extensive use of the term “CD Ripping”, which means copying the audio from the CD digitally (bit for bit), as opposed to converting it to analog, and then let your sound card convert it back. Perhaps DVD Decryption is a better term to describe this process.
| | |
|
|
Post Reply |
Moderated by: Admins, Superusers |
»
Guides (open)
» Some information about video compression
First ]
