The OpenHarmony Codec HDI (Hardware Device Interface) driver framework implements video hardware encoding and decoding based on OpenMax standards. It provides foundational codec APIs to upper-layer media services to access capabilities such as component creation, parameter configuration, data buffering, and component lifecycle management. This enables processing of video data formats like YUV/RGB into encoded streams such as H.264/H.265, and vice versa.

Codec HDI Architecture

Built on the HDF (Hardware Driver Foundation) framework, the Codec HDI driver consists of:

• Codec HDI Callback Remote Service: An anonymous callback service for handling asynchronous events.
• Codec HDI Interface: Standard OpenMax-based APIs for hardware codec operasions.
• Codec HDI Adapter: Implementation layer that bridges HDI interfaces with OpenMax IL.
• OpenMax IL Interface: Direct interface to the OpenMax IL layer.
• Vendor Implementation: Manufacturer-specific OpenMax adaptation layer.
• Codec Hardware: Physical decoding/encoding devices.

Core Concepts

Before development, understand these key terms:

• Sampling Rate: Number of samples per second taken from a continuous signal, measured in Hertz (Hz).
• OpenMax IL: Standard for hardware/software codecs, enabling uniform interaction between applications and multimedia components.
• Frame Rate: Number of images transmitted per second, affecting visual smoothness.
• Bitrate: Amount of video data transmitted per unit time (kbps), influencing clarity and artifacts.
• Component: OpenMax IL component abstraction for video stream processing modules.

Constraints

Codec HDI is designed for standard systems only; other platforms are not supported. Interface constraints follow OpenMax IL specifications.

Development Guide

Use Case

Codec modules perform hardware video encoding/decoding, converting raw YUV/RGB data to compressed formats like H.264, and decoding compressed streams back to raw formats.

Interface Specifications

• icodec_component_manager.h

  Interface	Description
  CreateComponent(sptr& component, uint32_t& componentId, const std::string& compName, int64_t appData, const sptr& callbacks)	Instantiates a codec component.
  DestroyComponent(uint32_t componentId)	Destroys a codec component instance.

• icodec_component.h

  Interface	Description
  SendCommand(CodecCommandType cmd, uint32_t param, const std::vector<int8_t>& cmdData)	Sends commands to a component.
  GetParameter(uint32_t index, const std::vector<int8_t>& inParamStruct, std::vector<int8_t>& outParamStruct)	Retrieves component parameters.
  SetParameter(uint32_t index, const std::vector<int8_t>& paramStruct)	Configures component parameters.
  GetState(CodecStateType& state)	Queries component state.
  UseBuffer(uint32_t portIndex, const OmxCodecBuffer& inBuffer, OmxCodecBuffer& outBuffer)	Assigns buffers to componant ports.
  FreeBuffer(uint32_t portIndex, const OmxCodecBuffer& buffer)	Releases allocated buffers.
  EmptyThisBuffer(const OmxCodecBuffer& buffer)	Submits input buffers for encoding/decoding.
  FillThisBuffer(const OmxCodecBuffer& buffer)	Fills output buffers with processed data.

• icodec_callback.h

  Interface	Descripsion
  EventHandler(CodecEventType event, const EventInfo& info)	Reports component events.
  EmptyBufferDone(int64_t appData, const OmxCodecBuffer& buffer)	Notifies completion of input buffer processing.
  FillBufferDone(int64_t appData, const OmxCodecBuffer& buffer)	Notifies completion of output buffer filling.

Refer to the Codec driver repository for additional interfaces.

Development Steps

Codec HDI driver development involves:

Driver Registration and Initialization

Define the HdfDriverEntry structure for Codec HDI, implementing Bind, Init, and Release function pointers.

static struct HdfDriverEntry g_codecManagerDriverEntry = {
    .moduleVersion = 1,
    .moduleName = "codec_component_manager_service",
    .Bind = CodecManagerDriverBind,
    .Init = CodecManagerDriverInit,
    .Release = CodecManagerDriverRelease,
};

• CodecManagerDriverBind: Binds HDF device to host and registers the codec service.

static int CodecManagerDriverBind(struct HdfDeviceObject *devObj)
{
    CODEC_LOG_INFO("Binding Codec Manager Driver");

    auto *hostInstance = new (std::nothrow) CodecManagerHost;
    if (hostInstance == nullptr) {
        CODEC_LOG_ERROR("Failed to allocate host instance");
        return HDF_FAILURE;
    }

    hostInstance->ioService.Dispatch = CodecManagerDispatch;
    hostInstance->ioService.Open = NULL;
    hostInstance->ioService.Release = NULL;

    auto serviceImpl = ICodecComponentManager::Get(true);
    if (serviceImpl == nullptr) {
        CODEC_LOG_ERROR("Service implementation unavailable");
        delete hostInstance;
        return HDF_FAILURE;
    }

    hostInstance->stub = OHOS::HDI::ObjectCollector::GetInstance().GetOrNewObject(serviceImpl, ICodecComponentManager::GetDescriptor());
    if (hostInstance->stub == nullptr) {
        CODEC_LOG_ERROR("Stub object creation failed");
        delete hostInstance;
        return HDF_FAILURE;
    }

    devObj->service = &hostInstance->ioService;
    return HDF_SUCCESS;
}

• CodecManagerDriverInit: Loads configuration properties from HCS (HDF Configuration Source).

static int CodecManagerDriverInit(struct HdfDeviceObject *devObj)
{
    CODEC_LOG_INFO("Initializing Codec Manager Driver");
    // Load HCS configuration
    return HDF_SUCCESS;
}