Support:AJAVideo/ImplementationDetail

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AJA Video Implementation

This section describes the AJA Video implementation in more detail.

Note that "DVIO" refers to the Digital Vision Video Library used by Nucoda and Phoenix to interface to video I/O boards like AJA and DVS.

Mapping of Signals to SDI Ports

The SDI I/O is mapped as labelled on the Kona 3G, Kona 4, AJA Breakout Box and cables.

  • 4K or UHDTV modes will map all four links as output, starting with SDI 1 to 4.

HDMI Support

If the AJA video I/O card supports HDMI output using the selected format, video will automatically be output over HDMI in addition to SDI.

The DVIO AJA component will detect the capabilities of the downstream receiver attached to the HDMI port and configure the output accordingly, updating if the receiver changes while running. Specifically :

  • HDMI output will be set to 10 bits/component if the receiver supports that, otherwise 8 bits/component.
  • The protocol sent via the HDMI port will be switched between HDMI and DVI to match the receiver's expectations.

The HDMI output is always set to RGB, which all HDMI implementations are required to support (regardless of the receiver's support for YUV).

No option is provided to enable YUV over HDMI.

The Kona 3G supports 4K video (3840/4096x2160) over SDI but not HDMI. HDMI output is disabled while a 4K video format is selected, resulting in a green display on the attached HDMI receiver. Normal HDMI display will resume when a non-4K video format is selected.

Changes to I/O Mode Behaviour

The DVIO AJA component handles incompatibilities between video formats and the I/O mode configured by the user via the preferences.

The AJA component attempts to set up the desired video format and may adjust the requested I/O mode if necessary in order to achieve this. In such cases, it takes the I/O mode as specifying absolutely the available hardware connectivity and receiver functionality (i.e. dual-link connection and 3G support), while treating provision of RGB444 colour as desired rather than obligatory.

There are still cases where incompatibility can result in card set-up failure but fall-back options will be used wherever possible.

The following limitations and fall-back behaviours apply :

RGB444 is not supported for 720p, NTSC and PAL video formats and they never need more than 1.5 Gbit/s bandwidth.

  • Fall back to YUV422, single link, no 3G for these formats.

When YUV422 is requested, this is taken to indicate that only one physical link is present (or four if a 4K format is desired), without 3G support.

  • High frame rate (see below) 1080p or 4x1080p video formats can not be set as sufficient bandwidth is not available.

When RGB444 via dual-link is requested, this is taken to indicate that two physical links are present (or four if a 4K format is desired), without 3G support.

  • High frame rate 4x1080p video formats can not be set as sufficient bandwidth is not available (eight physical links would be required just for YUV422).
  • High frame rate 1080p video formats and normal frame rate 4x1080p video formats are supported but fall back to YUV422. Otherwise, RGB444 is provided.

When RGB444 via 3G level A is requested, this is taken to indicate that only one physical link is present (or four if a 4K format is desired), with 3G support.

  • It is assumed that 3G-supporting devices will support both levels A and B. It seems that the AJA cards support 3G level A only for high frame rate 1080p and 4x1080p video formats; we provide 3G level A for these formats but fall back to YUV422. For all other video formats, we fall back to 3G level B.

When RGB444 via 3G level B is requested, this is taken to indicate that only one physical link is present (or four if a 4K format is desired), with 3G support.

  • It is assumed that 3G-supporting devices will support both levels A and B. High frame rate 4x1080p video formats can't be implemented using 3G level B due to the way the card needs to be configured for high frame rates with 3G level B, so we fall back to 3G level A YUV422 for these formats.
  • High frame rate 1080p video formats are supported but fall back to YUV422. Otherwise, RGB444 is provided.

Note :

  • 12 bit/component I/O modes are not supported for AJA cards at this time.
  • By "high frame rate", we mean > 30fps, i.e. 50, 59.94 and 60 fps. "Normal frame rate" means 30 fps or less.