What's I frame, B Frame

[yoshi1668]

Can someone explain what's I frame, B frame etc. in the TMPG setting. Thanks.

[BJ_M]

Intraframes, or I-frames, are the independent frames of reference for an MPEG file. These occur roughly twice per second. I-frames require higher bitrates than the average for a given compression ratio. However, they "anchor" the video, allowing such basic functionality as shuttling. (By comparison, the JPEG images used in MJPEG encoding are all considered I-frames, which allows for frame-specific editing, but uses up much more disk space.) Surrounding I-frames in an MPEG video clip are P-frames (Predicted) and B-frames (Bi-Directional). P-frames are compressed with reference to a previous frame and may themselves be used as references; B-frames are compressed with reference to both a previous and a subsequent frame and thus cannot themselves be references. Since they refer to other frames, P- and B- frames do not need to be reconstructed from scratch, and they may be encoded using significantly higher rates of compression than I-frames. B-frames are the most tightly compressed images in an MPEG file.


for the most part i dont suggest changing the default settings if you are not sure of the results .. and if making a dvd - these settings are critical for compatibility .