1. 像素时钟频率
The HDMI specification defines the protocols, signals, electrical interfaces and mechanical requirements of the standard.[42] The maximum pixel clock rate for HDMI 1.0 was 165 MHz, which was sufficient to support 1080p and WUXGA (1920×1200) at 60 Hz. HDMI 1.3 increased that to 340 MHz, which allows for higher resolution (such as WQXGA, 2560×1600) across a single digital link.[43] An HDMI connection can either be single-link (type A/C) or dual-link (type B) and can have a video pixel rate of 25 MHz to 340 MHz (for a single-link connection) or 25 MHz to 680 MHz (for a dual-link connection).
2. 支持的video format, audio format。不支持subtitle：
To ensure baseline compatibility between different HDMI sources and displays (as well as backward compatibility with the electrically compatible DVI standard) all HDMI devices must support the sRGB color space at 8 bits per component.[48] Support for the YCbCr color space and higher color depths ("deep color") is optional. HDMI permits sRGB 4:4:4 (8–16 bits per component), xvYCC 4:4:4 (8–16 bits per component), YCbCr 4:4:4 (8–16 bits per component), or YCbCr 4:2:2 (8–12 bits per component).[49][50] The color spaces that can be used by HDMI are ITU-R BT.601, ITU-R BT.709-5 and IEC 61966-2-4.[49]
For digital audio, if an HDMI device supports audio, it is required to support the baseline format: stereo (uncompressed) PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192 kHz.[20][51] HDMI also supports any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD.[51] With version 1.3, HDMI supports lossless compressed audio streams Dolby TrueHD and DTS-HD Master Audio.[51] As with the YCbCr video, device support for audio is optional. Audio Return Channel (ARC) is a feature introduced in the HDMI 1.4 standard.[52] "Return" refers to the case where the audio comes from the TV and can be sent "upstream" to the AV receiver using the HDMI cable connected to the AV receiver.[52] An example given on the HDMI website is that a TV that directly receives a terrestrial/satellite broadcast, or has a video source built in, sends the audio "upstream" to the AV receiver.[52]
The HDMI standard was not designed to pass closed caption data (for example, subtitles) to the television for decoding.[53] As such, any closed caption stream must be decoded and included as an image in the video stream(s) prior to transmission over an HDMI cable to be viewed on the DTV. This limits the caption style (even for digital captions) to only that decoded at the source prior to HDMI transmission. This also prevents closed captions when transmission over HDMI is required for upconversion. For example, a DVD player that sends an upscaled 720p/1080i format via HDMI to an HDTV has no way to pass Closed Captioning data so that the HDTV can decode it, as there is no line 21 VBI in that format.
3. HDMI 1.3 cable definition:
HDMI 1.3 defines two cable categories: Category 1-certified cables, which have been tested at 74.5 MHz (which would include resolutions such as 720p60 and 1080i60), and Category 2-certified cables, which have been tested at 340 MHz (which would include resolutions such as 1080p60 and 2160p30).[62][66][67] Category 1 HDMI cables are marketed as "Standard" and Category 2 HDMI cables as "High Speed".[1] This labeling guideline for HDMI cables went into effect on October 17, 20084. HDMI 1.4 cable definition:
- Standard HDMI Cable – up to 1080i and 720p
- Standard HDMI Cable with Ethernet
- Automotive HDMI Cable
- High Speed HDMI Cable – 1080p, 4K, 3D and deep color
- High Speed HDMI Cable with Ethernet
5. DDC
The Display Data Channel (DDC) is a communication channel based on the I²C bus specification.[81][82] HDMI specifically requires support for the Enhanced Display Data Channel (E-DDC), which is used by the HDMI source device to read the E-EDID data from the HDMI sink device to learn what audio/video formats it supports.[78][81][82] HDMI requires that the E-DDC support I²C standard mode speed (100 kbit/s) and allows optional support for fast mode speed (400 kbit/s).[83]
The DDC channel is actively used for High Definition Content Protection.
6. CEC
Consumer Electronics Control (CEC) is an HDMI feature designed to allow the user to command and control up-to ten CEC-enabled devices, that are connected through HDMI,[92][93] by using only one of their remote controls (for example by controlling a television set, set-top box, and DVD player using only the remote control of the TV).[94] CEC also allows for individual CEC-enabled devices to command and control each other without user intervention.[94][95][96][97][98][99][100]
It is a one-wire bidirectional serial bus that uses the industry-standard AV.link protocol to perform remote control functions. CEC wiring is mandatory, although implementation of CEC in a product is optional.
Trade names for CEC are Anynet+ (Samsung); Aquos Link (Sharp); BRAVIA Link and BRAVIA Sync (Sony); HDMI-CEC (Hitachi); E-link (AOC); Kuro Link (Pioneer); CE-Link and Regza Link (Toshiba); RIHD (Remote Interactive over HDMI) (Onkyo); RuncoLink (Runco International); SimpLink (LG); HDAVI Control, EZ-Sync, VIERA Link (Panasonic); EasyLink (Philips); and NetCommand for HDMI (Mitsubishi).[109][110][111][112][113]
The following is a list of HDMI-CEC commands:
- One Touch Play: allows devices to switch the TV to use it as the active source when playback starts
- System Standby enables users to switch multiple devices to standby mode with the press of one button
- Preset Transfer: transfers the tuner channel setup to another TV set
- One Touch Record allows users to record whatever is currently being shown on the HDTV screen on a selected recording device
- Timer Programming allows users to use the electronic program guides (EPGs) that are built into many HDTVs and set-top-boxes to program the timer in recording devices like PVRs and DVRs
- System Information: checks all components for bus addresses and configuration
- Deck Control allows a component to interrogate and control the operation (play, pause, rewind etc.), of a playback component (Blu-ray or HD DVD player or a Camcorder, etc.)
- Tuner Control allows a component to control the tuner of another component
- OSD Display: use the OSD of the TV set to display text
- Device Menu Control allows a component to control the menu system of another component by passing through the user interface (UI) commands
- Routing Control: control the switching of signal sources
- Remote Control Pass Through allows remote control commands to be passed through to other devices within the system
- Device OSD Name Transfer: transfer the preferred device names to the TV set
- System Audio Control allows the volume of an AV receiver, integrated amplifier or pre-amplifier to be controlled using any remote control from a suitably-equipped device(s) in the system
7. ARC和HEC (1.4 defined)
ARC就是可以把HDMI中的audio route到功放（av receiver上），这样就省了一根线（从media source连到功放的线）。配合CEC，美好的蓝图就是将所有设备都通过HDMI连接起来，然后一切就都搞定了。
HDMI 1.4 introduces two features called ARC (Audio Return Channel) and HEC (HDMI Ethernet Channel).[79][80][114] These features use two pins from the connector: a previously unused pin and the hot plug detect pin.[114]
ARC is an audio link meant to replace other cables between the TV and the A/V receiver or speaker system.[79] This direction is used when the TV is the one that generates or receives the video stream instead of the other equipment.[79]A typical case is the reception of ATSC or DVB signals by a TV, but reproduction of audio is handled by the other equipment.[79] Without ARC, the audio output from the TV needs to be routed by another cable, typically TOS-Link or coax, into the speaker system.[79]
HEC provides a bidirectional Ethernet communication at 100 Mbit/s.[80] It also goes by the name HEAC (HDMI, Ethernet, Audio, Control).[114]