Ripping Glossary by Doom9This is not meant to be a comprehensive and completely accurate description of most terms concerning DVD ripping but it should help you get the general idea. It may also not be completely accurate and I deliberately simplified some stuff. Mail me if you think I got something wrong or if you know of any good addition.
AuthenticationBefore a movie can be played the player and the disc have to establish a secured communication line on which they can transfer the actual movie. Before they can establish that line they need to make sure that the right "person" is on the other side - this is done via several key exchanges, verifications, etc. ASFAdvanced Streaming Format. Microsoft's answer to Real Media and streaming media in general. AVIAudio Video Interleave. The video format most commonly used on Windows pc's. It defines how video and audio are attached to each other, without specifying a codec. CodecCOder/DECoder. A codec is a piece of software that allows you to encode something - usually audio or video - to a specific format and can decode media encoded in this specific format again. Popular Codecs: MPEG1, MPEG2, MPEG-4, Indeo, etc. AVI, ASF, etc is not a codec but a format - that can be encoded using different codecs. DemultiplexingThe opposite of multiplexing. In this process a combined audio/video stream will be separated into the number of streams it consists of (a video stream, at least one audio stream and a navigational stream). Every VOB encoder demultiplexes the VOB files before encoding (FlaskMpeg, mpeg2avi, dvd2mpg, ReMpeg2) and every DVD player does the same (audio and video are being treated by different circuits, or decoded by different filters on a pc). DescramblingDVDs are usually CSS scrambled - imagine you decide to give a number to each letter, starting with 1 for a, etc. A sentence would become a couple of digits - that's what we call scrambled. Of course CSS is much better than that but it's still quite easy to crack. Descrambling means reversing the scrambling process, rendering our digits to a sentence again, or making our movie playable again - you can try to copy a movie to your hard disk when you've authenticated your DVD drive and play it, you'll get a garbled picture because it's still scrambled. Common CSS descramblers either use a pool of known descrambling keys (DeCSS or DODSrip - they contain a large number of keys but not all of them) or try to derive the key by a cryptographic attack (VobDec - that's why it works on most disc since it's not dependent on a pool of discs). Digital VideoDigital video is usually compressed since it'd take Terabytes - thousands of Gigabytes or for the mathematicians among you : 10^12 Bytes) to store a movie uncompressed. Since standard loss less compression is insufficient for video, the video codecs have to get rid of unimportant information - stuff the human eye won't see or is unlikely to see. Since that is still not enough modern compression algorithms use keyframes, I and P frames in order to save space. DivXNot to be confused with the now - thank God - obsolete DIVX (DIgital Video eXpress) system introduced by Circuit City '98. DivX is the name of the hacked Microsoft Mpeg4 codecs (Windows Media Video V3). Those codecs were developed by Microsoft for use in it's proprietary Windows Media architecture and initially supported encoding AVIs and ASFs but all non-beta versions included an AVI lock, making it impossible to use them to encode to the AVI format - and only a few tools support ASF today. What the makers of DivX did is remove that AVI lock making it possible to encode to AVI again, and changed the name to DivX video in order to prevent confusion of codecs, since it's possible to have both the unhacked and hacked codecs on the same computer if you use the Windows Media Encoder. The latest releases of DivX also include a hacked Windows Media Audio Codec called DivX audio - the hack of that codec is not perfect yet and it's use is limited for higher bitrates. DIVXDIVX was basically DVD stripped of all it's extra features - no extras, making-ofs, trailers, multi-language, widescreen picture - introduced by Circuit City and a bunch of greedy Hollywood lawyers in order to completely control movie distribution up to the end user again and to gain complete control over movie playback in your home. DIVX was pay-per-view and a "DIVX-enhanced" DVD player had to be hooked up to your phone line in order to dial in to the DIVX central computer to register when you play a disc and to bill your credit card. A movie was $4.50 - including a 48 hour viewing period - and $2.50 for additional viewing periods. DIVX was stopped after less than a year in operation due to lack of titles (Warner, Sony, New Line, and all the other smaller studios flatly refused to release any titles to the format - THANKS GUYS!!!) and the very negative press it got, mainly from DVD sites on the internet which later made it into serious printed publications and TV news. Formats used for DVD conversion
FrameThe basic source of a movie. One frame represents one image. A movie usually runs at 24 frames per seconds, so it has 24 different images per second. Imagine 24 images with a bird on it, in the first image it's on the left, then it gradually movies somewhat to the right. On the 24th frame the bird is on the right end of the image. Imagine these 24 images being played in sequence fast enough and it looks like a bird would fly from left to right to the human eye. I and P FramesFrame describing only the differences to the frame before (this is less than accurate but I think you'll get the picture that way). Say we have a keyframe with a bird before a cloudy sky. Then we can use I frames which say something like this : move the bird an inch to the left and one inch to the bottom. iDCT & WaveletThe video information inside MPEG files is stored in the frequency domain
rather than in the spatial domain (the images we see). That way, the information
gets compacted and that compactation can be used to compress (reduce)
the amount of information you have to send over the transmission channel.
MPEG uses the DCT (Discrete Cosine Transform) to translate spatial information
into frequency information. Wavelets are an alternative basis space. There are infinitely many wavelet bases (Daubechies, Haar, Mexican Hat, "Spline", Zebra, etc), but their primary feature is that they are localized. Fourier basis functions span all space (from negative to positive infinity). Wavelets are basically individual pulses of waves (at various positions and scales). Their value in compression stems from factors like the grouping which generally shows that a good 90% of the data is modelled by the low-pass filters, with the high-pass filters generally showing very small values that are mostly details. (of course, this is not true if the source is noisy in the first place). For images, the greatest value comes from localization of the basis, which means that we can model discontinuities (e.g. edges) VERY well with wavelets. You will NOT get those weird JPEG halos if you use wavelets InterleavingImagine gluing together the audio and the video track at defined points, that's about it. The player will recognize the interleave points and make sure that both audio and video are played in a manner that the "glued" points match thru the movie. Inverse TelecineThe inverse of Telecine. This process is performed to extract the original 24fps of a 29.97fps source. KeyframeA complete frame but heavily compressed. MPEGMPEG means Motion Picture Expert Group and it's THE resource for video formats in general. This group defines standards in digital video, among it the MPEG1 standard (used in Video CDs), the MPEG2 standard (used on DVDs and SVCDs), the MPEG4 standard and several audio standards - among them MP3 and AAC. MPEG4MPEG4 is pretty much a collection of standards defined by the MPEG Group, and it should become the next standard in digital video (mainly for picture phones, streaming media on the internet and more). MPEG4 allows the use of different encoding methods, for instance a keyframe can be encoded using ICT or Wavelets resulting in different output qualities. MultiplexingUsually video and audio are encoded separately. Then you have to join both of them to make a movie that you can play (you can of course play audio and video separately in two players but to get synch would be rather hard). During multiplexing the audio and video track are combined to one audio/video stream. The audio and video stream will be like woven together and navigational information will be added so that the player can example fast forward/backward and still retain synch audio/video. RippingLots of confusion about that one. Basically ripping means copying a DVD movie to your hard disk. This includes the authentication process for the DVD Drive (try to copy a file off a DVD and you'll get a message that this operation is not supported if your drive hasn't been authenticated) and the actual CSS Descrambling. CSS (Content Scrambling System) is a copy protection scheme designed to prevent unauthorized copying of DVD movies, although many argue that it was also designed to control where DVD movies can be played since without a CSS license you essentially have to crack the encryption to play a DVD movie - and I quite agree with that. The term "ripping" is also often used (even on this site) to describe the whole process of descrambling a DVD, then convert the audio and video into another - lesser - format. StreamlistA streamlist is an ASCII test file that
contains the pathnames and filenames of your VOB files, one file on every
line. Here's a small example: Save this file as streamlist.txt, or streamlist.lst. Make sure that you save it as unformatted ASCII text, I suggest you use notepad to edit your streamlists, since notepad won't save in another format. Mpeg2avi needs the streamlist to have the extension lst, whereas you're free to chose any other extension for other programs that use a streamlist. However the GUI is kind of limited in it's choice for input files/extensions, therefore you might have to rename your streamlist, if it doesn't show up in the file selection dialog. TelecineA process to bring a 24fps source (usually a movie is shot at that speed) to 29.97fps or 29.97x2 iterlaced fields per second. Please read this article on how the conversion actually works. Vob FilesAll DVD movies are stored in so-called VOB files. Vob files usually contain multiplexed Dolby Digital Audio and Mpeg2 video. Vob Files are called as follows: vts_XX_y.vob where XX represents the title and Y the part of the title. There can be 99 titles and 10 parts, although vts_XX_0.vob does never contain any video, usually just menu or navigational information. There's 2 ways to find out which files contain the main movie: First: Play the movie in any DVD player and watch the LED on a standalone or the status window on a software player. Second: The main movie is the largest number of consecutively numbered vob files. For instance it's vts_05_1.vob, vts_05_2.vob.... vts_05_8.vob (I haven't seen movies with 9 partial files but that doesn't mean that they don't exist). Windows MediaMicrosoft's proprietary architecture for audio and video on the pc. It's based on a collection of codecs which can be used by the WindowsMedia Player to play files encoded in any supported format. The current release of the Windows Media Player is version 7.0. WindowsMedia 7.0 offers a new set of codecs, among them a fully ISO compliant MPEG4 codec (called MS Windows Video V1), an improved MPEG-4 codec called MS Video V7 (although I did not notice any improvement compared with MS Windows Video V3 on which DivX is based), an encoder that supports Deinterlacing and Inverse Telecine. |