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T351 Week 12 - Spring 2008 Misc Announcements
Agenda:
Readings:
Video Codecs Interframe verses Intraframe Only the highest end video is uncompressed. Almost all video (especially HD) uses some sort of compression. When trying to understand the characteristics of various video recording gear, it's important to understand the basic differences between two general types of compression. Most standard definition tv codecs use some type of intraframe compression. This is where we take each individual frame and squeeze it so it all fits onto tape or disk. Examples of intraframe codecs include:
The nice thing about most intraframe recording is that it can be compressed and played back in real-time using inexpensive hardware. However many new HDV recorders are using interframe compression. The important thing to understand about interframe compression is that it compresses over time as well as space. In intraframe compression we divide the picture into smaller rectangles called macroblocks. These macroblocks are compressed and tracked over time and placed into a GOP (Group of Pictures) Examples of interframe codecs include:
MPEG-2 is a popular interframe codec. It is a very efficient in that it can squeeze a high definition video image into the same amount of space that a standard DV stream can occupy. (That's why we can record HDV onto a miniDV tape.) The other interesting thing about MPEG-2 is that it's scalable- we can make the frame dimensions varying sizes (720 x 480, 1440 x 1080 etc.). The down side is that GOPS can be difficult to edit. Deconstructing the GOPs during the edit process tasks the computers to a greater degree than intraframe codecs. Video for Multimedia Video from a non-linear editor often needs to be converted for uses other than television. Other uses include:
Each of these applications use a variety of different codecs and technologies. In most cases you can output your video through Quicktime to the appropriate codec. Sometimes you need specialized or proprietary hardware or software. Video DVDs use the MPEG-2 codec. There are both hardware and software converters. Many hardware converters can process in real-time. Software converters take longer but can provide high-quality results. Video games & software: New computer-based and console games can playback MPEG video. Early software used the Cinepak codec, now the Sorenson codec is frequently used. The Internet supports three competing architectures: Windows, Quicktime & Real. Websites often offer video at vaying bandwidths, but often use just one of the three architectures. You've discoveed this if you've ever found that you couldn't play video from a website untll installing the right plug-in for your browser Examples:
Format Conversion Editors will have to deal with a number of different media formats and need to understand the physical distinction between them. Some of the different formats include film, standard definition and high definition versions of NTSC, PAL, 16 x 9 and 4 x 3. NTSC (National Television Systems Committee) definition of standard definition TV, (used in North America, some of South America, Japan, etc) uses a frame rate close to 30, roughly 29.97 frames per second. There are 525 scan lines; approximately 480 of these are visible. The HD (high definition) standard for broadcast has been created by the ATSC, the Advanced Television Systems Committee, which was formed at the urging of the FCC to establish standards for the new high definition formats. PAL (Phase Alternate Line) is used in most of Europe, Australia, & Asia and runs at 25 frames per second using 625 lines. SECAM (Sequential Color and Memory) If possible it’s best to edit in the media’s native format. If you have high-quality PAL footage, it’s best to try to keep it in PAL. If you have 24 fps footage, it’s best to keep it in 24 fps. That way you won’t get conversion artifacts from changing frame rates and generation losses. But while ideal, we can’t always practice this. Often we’ll get a tape from another country, or that contains another type of media that must be integrated into our existing content. Anamorphic 16 x 9 is widescreen video that has been recorded into a 4:3 frame How can you get from one format to another? You can use hardware or software. Hardware
Software
Film to Video When converting film or 24p video to 60i (29.97) video we use a 3:2 Pulldown See Film runs at 24 frames per second. 24p refers to video shot at 24 frames per second progressive- that means there are no fields. Since film runs at 24 fps and video runs about 30 fps, the two aren't directly interchangeable at least on a frame for frame basis. (To be more precise, 23.976 film frames become 29.97 video frames.) In order to transfer film to 30 fps video, the film frames must be precisely sequenced into a combination of video frames and fields. A telecine is a piece of hardware containing a film projector sequenced with a video capture system. The telecine process is a term used to describe the process of converting film to video, also called a 3 2 pulldown. In the 3-2 pulldown each frame of film gets converted to 2 or 3 fields of video. Note how 4 (24fps) frames are converted to 5 interlaced frames (30 fps).
The problem with converting film frames to fields, is that some video frames have fields from two different film frames. If you think about it you'll see that this can present all types of problems. Apple makes a nice product that works with Final Cut Pro, Apple Cinema Tools, which includes a number of tools that can help convert 24 to 30 and back. Another method is to transfer film to 24p video. DTV (Digital TV broadcasting) TV Broadcasters are supposed to broadcast totally in digital by 2006, so the analog spectrum can be reclaimed for other purposes. DTV doesn't necessarily mean high-definition. DTV broadcasts can be either HD (High Definition) or SD (standard definition). You can squeeze 4 SD programs in the same space used to broadcast one HD program. Both use MPEG-2 compression. SD vs. HD SD works in both 4:3 and 16:9. Its video pixel dimensions include: HD is 16:9. Its video pixel dimensions include: Video frame rates: 24p, 30p, 30i, 60p, or 60i. HD has 4 discreet channels of audio. Beside having more pixel resolution, HD can display much more information in terms of color and brightness. HD has a much larger contrast ration than SD. It's not film, but it's getting close. Cybercollege reading: http://www.cybercollege.com/dtv_stans.htm Wanna shoot or edit in 16 x 9 or HiDef? See:
First you'll need to generate some source footage. Get your hands on the Panasonic AJ-HDC27 Varicam or Sony’s HDW-F900. Expect to pay about $200,000 for the camera with some decent glass. Editing in HD You can edit HD with Final Cut Pro. However don't expect to be able to view your work unless you have an HD breakout box of some sort. A few systems out there now include:
You can output Panasonic's DVCPRO HD and HDV in real-time through the firewire port. If you have a deck hooked up this can give you a way to view your content while you edit. You can also buy HD systems from a number of other vendors:
Metadata & Closed Captioning Metadata is embedded infotmation about the program itself (such as the title, running time, production notes, etc). Closed-captioning is text that can be displayed on screen for the hearing-impaired. Carried in the vertical blanking interval, the FCC mandates that all stations broadcast programming with closed captioning data. In addition, with the advent of interactive or enhanced TV, there is quite a bit of information that can be packaged within the video signal. For instance you might want to embed information on audio dialog levels, digital rights management (DRM) data, program running time, products, actors, production notes etc into the program content, which, with the right systems be viewed by viewers with interactive-capable sets. Avid makes Metasync, a product which let's editors work with this data right in the timeline. If you watch closed-captionined programming, you'll see a variety of levels in terms of readability, placement and propoer duration. Companies like Soft NI create stand-alone subtitler systems that let you integrate subtitles into a video stream. Adding subtitles involves propoer placement on the screen. Softel-USA makes products for subtitling HD programming. Vocabulary (Know these terms)
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