P Frame
A P-frame is a video frame encoded relative to the past reference frame. A reference frame is a P- or I-frame. The past reference frame is the closest preceding reference frame.

Each macroblock in a P-frame can be encoded either as an I-macroblock or as a P-macroblock. An I-macroblock is encoded just like a macroblock in an I-frame. A P-macroblock is encoded as a 16x16 area of the past reference frame, plus an error term. To specify the 16x16 area of the reference frame, a motion vector is included. A motion vector (0, 0) means that the 16x16 area is in the same position as the macroblock we are encoding. Other motion vectors are relative to that position. Motion vectors may include half-pixel values, in which case pixels are averaged. The error term is encoded using the DCT, quantization, and run-length encoding. A macroblock may also be skipped which is equivalent to a (0, 0) vector and an all-zero error term. The search for good motion vector (the one that gives small error term and good compression) is the heart of any MPEG-1 video encoder and it is the primary reason why encoders are slow. MPEG FAQ

PAL
Short for Phase Alternating Line, the dominant television standard in Europe. The United States uses a different standard, NTSC. PAL delivers 625 lines at 50 fields (half-frames interlaced) per second. The resolution of a PAL VCD is 352x288 pixels, a PAL SVCD is 480x576, and a PAL full D1 DVD is 704 or 720 x 576.



Pan & Scan
The technique of reframing a picture to conform to a different aspect ratio by cropping parts of the picture. DVD-Video players can automatically create a 4:3 pan & scan version from widescreen video by using a horizontal offset encoded with the video, which allows the focus of attention to always be visible.



PBC
Playback control, PBC, is available for Video CD (VCD) 2.0 and Super Video CD (SVCD) 1.0 disc formats. PBC allows control of the playback of play items and the possibility of interaction with the user through the remote control or some other input device available.


Perceptual Coding
Lossy compression techniques based on the study of human perception. Perceptual coding systems identify and remove information that is least likely to be missed by the average human observer.

Physical Sector Number
Serial number assigned to physical sectors on a DVD disc. Serial incremented numbers are assigned to sectors from the head sector in the Data Area as 30000h from the start of the Lead In Area to the end of the Lead Out Area.


Pixel
The smallest picture element of an image (one sample of each color component). A single dot of the array of dots that makes up a picture. Sometimes abbreviated to pel. The resolution of a digital display is typically specified in terms of pixels (width by height) and color depth (the number of bits required to represent each pixel).



Pixel Aspect Ratio
The ratio of width to height of a single pixel. Often means sample pitch aspect ratio (when referring to sampled digital video). Pixel aspect ratio for a given raster can be calculated as y/x multiplied by w/h (where x and y are the raster horizontal pixel count and vertical pixel count, and w and h are the display aspect ratio width and height). Pixel aspect ratios are also confusingly calculated as x/y multiplied by w/h, giving a height-to-width ratio.

Premastering
The process of preparing data in the final format to create a DVD disc image for mastering. Includes creating DVD control and navigation data, multiplexing data streams together, generating error-correction codes, and performing channel modulation. Often includes the process of encoding video, audio, and subpictures.

Pro-Logic
An encoding technology developed by Dolby Laboratories, Pro-Logic and Pro-Logic II are methods of encoding 4 channels for Pro-Logic (left, right, center, surround) and 5 channels for Pro-Logic II (left, right, center, left surround, right surround), into a stereo (left, right) channel format to be decoded into 4 or 5 channels with a proper decoder. It is actually just a small amount of inaudible data slipped into a stereo audio stream that can be recognized by a decoder so that the decoder can separate the stereo signal into 4 or 5 channels. A Pro-Logic signal can be encoded into any form of stereo audio stream including digital files such as mpeg-1/2 layer 2, MP3, uncompressed PCM, audio CD's, and it is also used to get multichannel in VHS tapes and other analog sources. You can listen to Pro-Logic encoded audio streams with any normal equitment but you will only have 2 channels. DVD players are required to have a capable Dolby Digital decoder to downmix a 5.1 Dolby Digital signal on DVDs to a Pro-Logic stereo signal to be output with analog RCA cables. Pro-Logic II can be decoded with Pro-Logic decoders but you will only get 4 channels instead of 5. Pro-Logic is also called Dolby Surround. Dolby

Program Stream
A program stream is the combination of individual audio and video elementary streams, into a single file. Each of the elementary streams in broken up into multiple variable length packets known as Packetized Elementary Streams (PES). A program stream is suitable for use where transmission errors are relatively rare, such as a DVD or hard disk file.

Progressive Scan
A video scanning system that displays all lines of a frame in one pass. Contrast with interlaced scan. 

Pulldown
Film is generally shot and projected at 24 frames per second (fps), so when film frames are converted to NTSC video, the rate must be modified to play at 29.97 fps. During the telecine process, twelve (12) fields are added to each 24 frames of film (12 fields = 6 frames) so the same images that made up 24 frames of film then comprise 30 frames of video.Video plays at a speed of 29.97 fps so the film actually runs at 23.976 fps when transferred to video.

AVID does a 2-3 pulldown (which is used in a lot of film editing)

But most other editors use 3-2 pulldown.

2-3 Pulldown vs. 3-2
It is commonly referred to as 3-2 pulldown; while modern telecine machines can go either way. Therefore, AA BB BC CD DD. If the telecine is set for 3-2, you'll get BB BC CD DD AA.

Another slightly confusing consideration: When the pulldown process occurs, it turns out that the video version of the film runs slightly SLOWER than the original film did. This occurs because the film is running at 24 frames per second, but in order to create the right pattern of A-B-C-D on the video tape, which runs at 29.97 frames per second, the film was actually played at 23.976 fps during the telecine (film->tape process).

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