Hi,
I know mpeg videos are composed of I, B, and P frames. What do the letters stand for? I know B stands for bi-directional. Does "I" stand for inter-frame, and "P" for prediction? I've done some video editing in Ulead Video Studio. Are "I" frames similar to AVI keyframes whereas B and P frames are delta frames?
I don't know much about it or if this will help, but this is what I found off Google:
MPEG Frame Types 1 – I frames
Intra-coded images
Similar to a JPEG still of the frame
Expensive but required
I-frames are expensive as they have to compress the entire scene in one shot
Needed as start frame
Needed for scene changes
MPEG Frame Types 2 – P frames
Predictive coded frames
Based on predicting the movement of blocks from their position in the previous frame (I or P).
IPPPPIPPP
Typically send at least 1 I frame per 16 frames.
MPEG Frame Types 3 – B frames
Bi-directional frames
Based either on the previous I/P frame or on the next I/P frame – whichever is closest!
IBBPBIBBP
Typically only two B frames in a row.
Presentation v coding order
# As an intraframe, which contains the complete image data for that frame. This method of encoding provides the least compression.
# As a predicted frame, which contains just enough information to tell the DVD player how to display the frame based on the most recently displayed intraframe or predicted frame. This means that the frame contains only the data that relates to how the picture has changed from the previous frame.
# As a bidirectional frame. In order to display this type of frame, the player must have the information from the surrounding intraframe or predicted frames. Using data from the closest surrounding frames, it uses interpolation, which is sort of like averaging, to calculate the position and color of each pixel.
An I frame is a single image from a video stream that is compressed in a procedure that is similar to a JPEG, i.e. the entire image is used. If every image in a film were to be compressed individually, the typically high compression factor of MPEG-4/DivX would not be reached. That is why P frames are also used. We can explain the principle of prediction by way of an example: imagine the anchorperson of a news broadcasting station. For the most part, the background does not change while the newscaster moves in the foreground. Here you could leave out the redundant background and simply describe the changes by means of instructions for specific areas of the image. The image is divided into individual blocks to do this. The time differences are represented in the P frame by precisely these changes from block to block.
