如何在Directshow中使用硬解码功能

本文主要是介绍如何在Directshow中使用硬解码功能，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

    在Directshow中使用硬解码一般通过DXVA技术，这是微软针对Windows系统定义的硬件加速解码的一个标准接口，目前很多显卡厂商已经实现了。通过DXVA接口，我们以一种统一的接口形式访问各种显卡的硬件加速（解码）功能，还可以通过API接口设置参数来控制解码的一些流程。但这篇博文不是给大家讲怎么用DXVA API来解码视频，而是介绍另外一种简单的方法：通过LAV Video Decoder。这是一个Directshow解码器插件，是开源的LAV Filters里面的一个子插件。

   LAVVideo即支持软解码，也支持硬解码（封装了DXVA接口），并且Filter提供接口给外部设置解码器的一些参数。下载LAV Filters的二进制文件包，里面有个developer_info目录，进去找到LAVVideoSettings.h，这个头文件声明了LAVVideo Decode Filter实现的接口。这个类的声明如下：

// LAV Video configuration interface
[uuid("FA40D6E9-4D38-4761-ADD2-71A9EC5FD32F")]
interface ILAVVideoSettings : public IUnknown
{// Switch to Runtime Config mode. This will reset all settings to default, and no changes to the settings will be saved// You can use this to programmatically configure LAV Video without interfering with the users settings in the registry.// Subsequent calls to this function will reset all settings back to defaults, even if the mode does not change.//// Note that calling this function during playback is not supported and may exhibit undocumented behaviour. // For smooth operations, it must be called before LAV Video is connected to other filters.STDMETHOD(SetRuntimeConfig)(BOOL bRuntimeConfig) = 0;// Configure which codecs are enabled// If vCodec is invalid (possibly a version difference), Get will return FALSE, and Set E_FAIL.STDMETHOD_(BOOL,GetFormatConfiguration)(LAVVideoCodec vCodec) = 0;STDMETHOD(SetFormatConfiguration)(LAVVideoCodec vCodec, BOOL bEnabled) = 0;// Set the number of threads to use for Multi-Threaded decoding (where available)//  0 = Auto Detect (based on number of CPU cores)//  1 = 1 Thread -- No Multi-Threading// >1 = Multi-Threading with the specified number of threadsSTDMETHOD(SetNumThreads)(DWORD dwNum) = 0;// Get the number of threads to use for Multi-Threaded decoding (where available)//  0 = Auto Detect (based on number of CPU cores)//  1 = 1 Thread -- No Multi-Threading// >1 = Multi-Threading with the specified number of threadsSTDMETHOD_(DWORD,GetNumThreads)() = 0;// Set whether the aspect ratio encoded in the stream should be forwarded to the renderer,// or the aspect ratio specified by the source filter should be kept.// 0 = AR from the source filter// 1 = AR from the Stream// 2 = AR from stream if source is not reliableSTDMETHOD(SetStreamAR)(DWORD bStreamAR) = 0;// Get whether the aspect ratio encoded in the stream should be forwarded to the renderer,// or the aspect ratio specified by the source filter should be kept.// 0 = AR from the source filter// 1 = AR from the Stream// 2 = AR from stream if source is not reliableSTDMETHOD_(DWORD,GetStreamAR)() = 0;// Configure which pixel formats are enabled for output// If pixFmt is invalid, Get will return FALSE and Set E_FAILSTDMETHOD_(BOOL,GetPixelFormat)(LAVOutPixFmts pixFmt) = 0;STDMETHOD(SetPixelFormat)(LAVOutPixFmts pixFmt, BOOL bEnabled) = 0;// Set the RGB output range for the YUV->RGB conversion// 0 = Auto (same as input), 1 = Limited (16-235), 2 = Full (0-255)STDMETHOD(SetRGBOutputRange)(DWORD dwRange) = 0;// Get the RGB output range for the YUV->RGB conversion// 0 = Auto (same as input), 1 = Limited (16-235), 2 = Full (0-255)STDMETHOD_(DWORD,GetRGBOutputRange)() = 0;// Set the deinterlacing field order of the hardware decoderSTDMETHOD(SetDeintFieldOrder)(LAVDeintFieldOrder fieldOrder) = 0;// get the deinterlacing field order of the hardware decoderSTDMETHOD_(LAVDeintFieldOrder, GetDeintFieldOrder)() = 0;// DEPRECATED, use SetDeinterlacingModeSTDMETHOD(SetDeintAggressive)(BOOL bAggressive) = 0;// DEPRECATED, use GetDeinterlacingModeSTDMETHOD_(BOOL, GetDeintAggressive)() = 0;// DEPRECATED, use SetDeinterlacingModeSTDMETHOD(SetDeintForce)(BOOL bForce) = 0;// DEPRECATED, use GetDeinterlacingModeSTDMETHOD_(BOOL, GetDeintForce)() = 0;// Check if the specified HWAccel is supported// Note: This will usually only check the availability of the required libraries (ie. for NVIDIA if a recent enough NVIDIA driver is installed)// and not check actual hardware support// Returns: 0 = Unsupported, 1 = Supported, 2 = Currently runningSTDMETHOD_(DWORD,CheckHWAccelSupport)(LAVHWAccel hwAccel) = 0;// Set which HW Accel method is used// See LAVHWAccel for options.STDMETHOD(SetHWAccel)(LAVHWAccel hwAccel) = 0;// Get which HW Accel method is activeSTDMETHOD_(LAVHWAccel, GetHWAccel)() = 0;// Set which codecs should use HW AccelerationSTDMETHOD(SetHWAccelCodec)(LAVVideoHWCodec hwAccelCodec, BOOL bEnabled) = 0;// Get which codecs should use HW AccelerationSTDMETHOD_(BOOL, GetHWAccelCodec)(LAVVideoHWCodec hwAccelCodec) = 0;// Set the deinterlacing mode used by the hardware decoderSTDMETHOD(SetHWAccelDeintMode)(LAVHWDeintModes deintMode) = 0;// Get the deinterlacing mode used by the hardware decoderSTDMETHOD_(LAVHWDeintModes, GetHWAccelDeintMode)() = 0;// Set the deinterlacing output for the hardware decoderSTDMETHOD(SetHWAccelDeintOutput)(LAVDeintOutput deintOutput) = 0;// Get the deinterlacing output for the hardware decoderSTDMETHOD_(LAVDeintOutput, GetHWAccelDeintOutput)() = 0;// Set whether the hardware decoder should force high-quality deinterlacing// Note: this option is not supported on all decoder implementations and/or all operating systemsSTDMETHOD(SetHWAccelDeintHQ)(BOOL bHQ) = 0;// Get whether the hardware decoder should force high-quality deinterlacing// Note: this option is not supported on all decoder implementations and/or all operating systemsSTDMETHOD_(BOOL, GetHWAccelDeintHQ)() = 0;// Set the software deinterlacing mode usedSTDMETHOD(SetSWDeintMode)(LAVSWDeintModes deintMode) = 0;// Get the software deinterlacing mode usedSTDMETHOD_(LAVSWDeintModes, GetSWDeintMode)() = 0;// Set the software deinterlacing outputSTDMETHOD(SetSWDeintOutput)(LAVDeintOutput deintOutput) = 0;// Get the software deinterlacing outputSTDMETHOD_(LAVDeintOutput, GetSWDeintOutput)() = 0;// DEPRECATED, use SetDeinterlacingModeSTDMETHOD(SetDeintTreatAsProgressive)(BOOL bEnabled) = 0;// DEPRECATED, use GetDeinterlacingModeSTDMETHOD_(BOOL, GetDeintTreatAsProgressive)() = 0;// Set the dithering mode usedSTDMETHOD(SetDitherMode)(LAVDitherMode ditherMode) = 0;// Get the dithering mode usedSTDMETHOD_(LAVDitherMode, GetDitherMode)() = 0;// Set if the MS WMV9 DMO Decoder should be used for VC-1/WMV3STDMETHOD(SetUseMSWMV9Decoder)(BOOL bEnabled) = 0;// Get if the MS WMV9 DMO Decoder should be used for VC-1/WMV3STDMETHOD_(BOOL, GetUseMSWMV9Decoder)() = 0;// Set if DVD Video support is enabledSTDMETHOD(SetDVDVideoSupport)(BOOL bEnabled) = 0;// Get if DVD Video support is enabledSTDMETHOD_(BOOL,GetDVDVideoSupport)() = 0;// Set the HW Accel Resolution Flags// flags: bitmask of LAVHWResFlag flagsSTDMETHOD(SetHWAccelResolutionFlags)(DWORD dwResFlags) = 0;// Get the HW Accel Resolution Flags// flags: bitmask of LAVHWResFlag flagsSTDMETHOD_(DWORD, GetHWAccelResolutionFlags)() = 0;// Toggle Tray IconSTDMETHOD(SetTrayIcon)(BOOL bEnabled) = 0;// Get Tray IconSTDMETHOD_(BOOL,GetTrayIcon)() = 0;// Set the Deint ModeSTDMETHOD(SetDeinterlacingMode)(LAVDeintMode deintMode) = 0;// Get the Deint ModeSTDMETHOD_(LAVDeintMode,GetDeinterlacingMode)() = 0;
};

我们主要关注SetHWAccel方法：  STDMETHOD(SetHWAccel)(LAVHWAccel hwAccel) = 0; 传入参数的类型LAVHWAccel的定义如下：

// Type of hardware accelerations
typedef enum LAVHWAccel {
  HWAccel_None,
  HWAccel_CUDA,
  HWAccel_QuickSync,
  HWAccel_DXVA2,
  HWAccel_DXVA2CopyBack = HWAccel_DXVA2,
  HWAccel_DXVA2Native

};

我们一般选HWAccel_DXVA2，通过这种方式解码后的数据放在显存，直接显示效率很高。

后面的工作就简单了。构建一个播放文件的Filter Graph，将LAVVideo Decoder与Video Renderer连接，记住Renderer必须是EVR，否则硬解将不能够生效或者解码时的CPU比较高。运行Filter Graph，然后打开任务管理器查看CPU，会发现播放所占用的CPU很低（在我的酷睿i3 CPU的机器上小于5%）。

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