I
IDR picture
When the decoder receives an IDR picture, all subsequent transmitted slices can be decoded without references to any frame decoded prior to IDR picture.
Image aspect ratio
The ratio of the width to the height of a frame of a video image. For conventional PAL/NTSC television standards, the aspect ratio is 4:3, or 1.333.
Impedance
The total of the resistive and reactive opposition, measured in ohms, that a circuit presents to the flow of alternating current at a given frequency.
Interlaced
A video storage mode consisting of fields (odd or even lines) with each field containing half of the lines in a frame.
I/O
Input/Output.
ISO
International Standards Organization.
ITU
International Telecommunications Union.