| |
What is HDMI Data?
There are three categories of data that is transmitted via an HDMI link.
Video Data-Video pixel data (8b data encoded to 10b), and Guard Bands (fixed 10b pattern).
Data Island-Packet data, which can be either audio samples or Infoframes (TERC4 encoded, 4b encoded to 10b) as well as its own Guard Band (fixed 10b pattern).
Control-Control period coding, in which we find HSYNC, VSYNC (2b to 10b encoding) and a Preamble (used to determine whether subsequent data is video or data island).
Transmission of Video / Graphics
HDMI transmits 24bit pixel data via three separate channels.
Pixel rates supported are 25MHz to 165MHz.
This is exactly the same as single link DVI 1.0
Also supports video rates below 25MHz eg 13.5MHz for 480i NTSC signals.
Achieves this through a "pixel-repetition" scheme.
Can handle pixel data in RGB, YCbCr (4-4-4), YCbCr (4-2-2) formats.
In all cases 24 bits of data per pixel clock are transmitted.
Transmission of Audio
Basic Audio is provided via an IEC60958 audio stream at 33kHz, 44.1kHz, or 48kHz.
Accommodates any normal stereo audio stream.
Optionally this stream can be sent as a single channel at 192kHz.
Can support IEC61937 compressed formats as found in surround-sound, Dolby Digital, etc. At rates up to 192kHz.
Infoframes and HDMI
EIA/CEA-861B specifies a special packet called an infoframe.
HDMI sources and sinks are expected to use two basic infoframes.
AVI (Auxiliary Video Information) Infoframe.
Communicates Colorimetry, Picture aspect ratio, Pixel-Repetition factor, RGB or YCbCrindicator, and others specified within 861B standard.
Audio Infoframe.
Communicates, Channel count, Coding Type, Sample size, Sample frequency, Channel allocation and other audio specific information.
There are other types of infoframes that are supported by the 861B standard, but are optional with respect to HDMI specification.
| |
