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Probing and Locking of Configurations

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The process for establishing the configuration for each DirectX VA function (a specific value of bDXVA_Func) that needs a configuration (for example, compressed picture decoding, alpha-blending data loading, and alpha-blending combination) can be performed by:

  1. Probing (if needed) to determine whether a configuration is accepted by the accelerator.

  2. Locking in a specific configuration, if it is supported.

To determine if a specific configuration is supported, a probing command is sent to the accelerator for the particular bDXVA_Func value to be probed, along with a configuration. In addition to the probing command, a configuration structure (for the value in bDXVA_Func) is sent that describes the configuration being probed to determine whether the configuration is supported. The accelerator then returns a value of S_OK or S_FALSE, indicating whether the specified configuration is supported by the accelerator. The accelerator can also return a suggested alternative configuration.

To lock in a specific configuration, a locking command is sent to the accelerator for the particular bDXVA_Func to be locked. Along with the locking command, a configuration structure (for the value in bDXVA_Func) is sent that describes the configuration to be locked in, if the configuration is supported. The accelerator returns an S_OK or S_FALSE indicating whether the specified configuration is supported by the accelerator. If the return value is S_OK, the specified configuration is locked in for use. If the return value is S_FALSE, a suggested alternative configuration is returned.

The decoder may send a locking command without first sending a probing command for the specified configuration. If the accelerator returns an S_OK in a probing command for a specific configuration, it returns an S_OK to a locking command for that same configuration, unless otherwise noted. After a locking command has been sent and the accelerator returns S_OK, the specified configuration is locked in and no additional probing or locking commands are sent by the decoder for the same value of bDXVA_Func.

To ensure that all DirectX VA software decoders can operate with all DirectX VA accelerators, a minimal interoperability configuration set is defined as a set of configurations that must be supported by any decoder using a particular value for bDXVA_Func. Every accelerator that indicates support for the bDXVA_Func variable by exposing an associated video accelerator GUID must support at least one member of this interoperability configuration set. In some cases, an additional encouraged configuration set may also be defined.

The following figure shows the control flow of probing and locking commands sent by the decoder.

Flowchart that shows the control flow of probing and locking commands sent by the decoder.