I, P and B Frames

There are three types of pictures (or frames) used in video compression: I‑frames, P‑frames, and B‑frames.

An I‑frame is an 'Intra-coded picture', in effect a fully specified picture, like a conventional static image file. P‑frames and B‑frames hold only part of the image information, so they need less space to store than an I‑frame, and thus improve video compression rates.

A P‑frame ('Predicted picture') holds only the changes in the image from the previous frame. For example, in a scene where a car moves across a stationary background, only the car's movements need to be encoded. The encoder does not need to store the unchanging background pixels in the P‑frame, thus saving space. P‑frames are also known as delta‑frames.

A B‑frame ('Bi-predictive picture') saves even more space by using differences between the current frame and both the preceding and following frames to specify its content.



http://en.wikipedia.org/wiki/Video_compression_picture_types

Compression

Data compression is the process of encoding information to reduce the number of bits as compared to the uncompressed version of the information. A compression process will reduce the disk space required to store the information, and bandwidth required to transmit information.
          Compression can be lossless or lossy. Video Compression used in security applications is lossy compression, meaning once the original video information is compressed it can never be decompressed to restore all of the original information. In lossy compression, if information is compressed then decompressed then recompressed and so on, more and more information will be lost with each successive compression.
Video information lends itself well to lossy compression techniques. The reason being, there is a significant amount of data the human eye does not perceive in the uncompressed version of the video or image. Image and video compression takes advantage of this fact.
          Specifically the human visual system perceives brightness more readily than color. If you have ever compared LCD televisions, you may have noticed displays with higher contrast ratios look better. The contrast ratio is the difference from the brightest white to the darkest black that can be displayed on the set. Since our visual system perceives differences in brightness more than color the effect is a more appealing display, which is the same effect JPEG compression takes advantage of.

Lossy and Lossless

Lossless and lossy compression are terms that describe whether or not, in the compression of a file, all original data can be recovered when the file is uncompressed. With lossless compression, every single bit of data that was originally in the file remains after the file is uncompressed. All of the information is completely restored. This is generally the technique of choice for text or spreadsheet files, where losing words or financial data could pose a problem. The Graphics Interchange File (GIF) is an image format used on the Web that provides lossless compression.
          On the other hand, lossy compression reduces a file by permanently eliminating certain information, especially redundant information. When the file is uncompressed, only a part of the original information is still there (although the user may not notice it). Lossy compression is generally used for video and sound, where a certain amount of information loss will not be detected by most users.

http://www.salientsys.com/files/whitepaper/Understanding%20H%20264.pdf

http://www.google.co.uk/#hl=en&q=video+compression&tbs=dfn:1&tbo=u&sa
=X&ei=SMArT4LAI4Lq8QO2wcThDg&ved=0CC0QkQ4&bav=on.2,or.r_gc.
r_pw.,cf.osb&fp=47ed5b9489390682&biw=1440&bih=705

http://searchcio-midmarket.techtarget.com/definition/lossless-and-lossy-compression

Interlace and De-Interlace

Interlace: A common way to compress video is to interlace it. Each frame of an interlaced video signal shows every other horizontal line of the image. As the frames are projected on the screen, the video signal alternates between showing even and odd lines. When this is done fast enough, i.e. around 60 frames per second, the video image looks smooth to the human eye.
          Interlacing has been used for decades in analog television broadcasts that are based on the NTSC (U.S.) and PAL (Europe) formats. Because only half the image is sent with each frame, interlaced video uses roughly half the bandwidth than it would sending the entire picture.

  Interlaced video frame consists of two sub-fields taken in sequence, each sequentially scanned at odd and even lines of the image sensor; analog television employed this technique because it allowed for less transmission bandwidth and further eliminated the perceived flicker that a similar frame rate would give using progressive scan. CRT based displays were able to display interlaced video correctly due to its complete analogue nature. All of the newer displays are inherently digital in that the display comprises discrete pixels. Consequently the two fields need to be combined into a single frame, which leads to various visual defects which the deinterlacing process should try to minimise.

Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form.
      

Second Video

I have now completed my second parkour video using a different style of music to the first. The feel of the piece has dramatically changed just by a simple music change and a re-arrange of the clips used.