Unlocking the Secrets of DXVA: Is there a way to scale NV12 surface decoded by DXVA?

As developers and multimedia enthusiasts, we’re constantly on the lookout for innovative ways to optimize and enhance our video playback experiences. One of the most popular and widely-used APIs for video decoding is DXVA (DirectX Video Acceleration). But, have you ever wondered, “Is there a way to scale NV12 surface decoded by DXVA?” In this comprehensive guide, we’ll delve into the world of DXVA, explore the NV12 surface, and provide clear instructions on how to scale it. Buckle up, and let’s dive in!

What is DXVA, and why do we need it?

DXVA is a set of APIs designed by Microsoft to enable hardware-accelerated video playback on Windows-based systems. It allows developers to offload computationally intensive video decoding tasks to the GPU, freeing up system resources and improving overall performance. With the increasing demand for high-quality video content, DXVA has become an essential tool for multimedia applications.

What is an NV12 surface?

An NV12 surface is a specific format of video frame data used in DXVA. It’s a planar format, where the luminance (Y) and chrominance (UV) components are stored separately. The NV12 format is widely supported by most graphics cards and is an efficient way to store and process video data.

The Challenge: Scaling an NV12 Surface Decoded by DXVA

So, why is scaling an NV12 surface decoded by DXVA a challenge? The issue lies in the fact that DXVA decodes the video data into an NV12 surface, which is not directly compatible with most graphics cards. To scale the video, we need to convert the NV12 surface to a format that can be processed by the GPU. This is where things get tricky.

The Conventional Approach: Copying and Converting the NV12 Surface

The traditional method of scaling an NV12 surface involves copying the decoded data and converting it to a different format, such as RGB or YUV. This approach has two major drawbacks:

• Performance: Copying and converting the data can be computationally expensive, leading to reduced performance and increased latency.
• Quality: The conversion process can lead to loss of video quality, especially if the original NV12 surface is not properly preserved.

A Better Approach: Using DXVA’s Built-in Scaling Capabilities

Fortunately, DXVA provides a built-in scaling mechanism that can be leveraged to resize the NV12 surface without the need for copying and converting the data. This approach is not only more efficient but also preserves the original video quality.

Step 1: Create a DXVA Device

To use DXVA’s scaling capabilities, we need to create a DXVA device. This can be done using the following code snippet:

// Create a DXVA device
DXVA_Device device;
hr = DXVA_CreateDevice(&device);

Step 2: Create a DXVA Video Decoder

Next, we need to create a DXVA video decoder. This will be responsible for decoding the video data into an NV12 surface:

// Create a DXVA video decoder
DXVA_VideoDecoder decoder;
hr = DXVA_CreateVideoDecoder(device, &decoder);

Step 3: Set the Decoded Surface Format

We need to specify the format of the decoded surface. In this case, we’ll use the NV12 format:

// Set the decoded surface format to NV12
DXVA_SurfaceDescription sd;
sd.Format = DXVA_SurfaceFormat_NV12;
hr = DXVA_SetDecodedSurfaceFormat(decoder, &sd);

Step 4: Decode the Video Data

Now, we can decode the video data using the DXVA video decoder:

// Decode the video data
hr = DXVA_DecodeVideoData(decoder, &decodedSurface);

Step 5: Scale the Decoded Surface

This is where the magic happens! We can use DXVA’s built-in scaling capabilities to resize the decoded NV12 surface:

// Create a DXVA scaling filter
DXVA_ScalingFilter sf;
hr = DXVA_CreateScalingFilter(device, &sf);

// Set the scaling filter properties
sfDSTRect.left = 0;
sfDSTRect.top = 0;
sfDstRect.right = scaledWidth;
sfDstRect.bottom = scaledHeight;
hr = DXVA_SetScalingFilterProperties(sf, &sfDSTRect);

// Scale the decoded surface
hr = DXVA_ScaleVideoSurface(sf, decodedSurface, &scaledSurface);

Step 6: Display the Scaled Surface

Finally, we can display the scaled NV12 surface using our preferred rendering method:

// Display the scaled surface
hr = RenderSurface(scaledSurface);

Conclusion

In this article, we’ve demonstrated a clear and efficient way to scale an NV12 surface decoded by DXVA. By leveraging DXVA’s built-in scaling capabilities, we can avoid the pitfalls of copying and converting the decoded data, ensuring optimal performance and video quality.

Frequently Asked Questions

• Q: Can I use DXVA with other video formats besides NV12?
• A: Yes, DXVA supports a wide range of video formats, including YV12, YUY2, and RGB.
• Q: What’s the minimum system requirement for using DXVA?
• A: DXVA requires a Windows-based system with a DirectX 9.0c-compatible graphics card.
• Q: Can I use DXVA for video encoding as well?
• A: No, DXVA is primarily designed for video decoding. For video encoding, you’ll need to use a different API or library.

Conclusion (Again!)

In conclusion, scaling an NV12 surface decoded by DXVA is not only possible but also efficient and effective when done correctly. By following the steps outlined in this guide, you’ll be well on your way to unlocking the full potential of DXVA and delivering exceptional video playback experiences.

DXVA Version	Supported Platform	Minimum System Requirements
DXVA 2.0	Windows Vista, Windows 7	DirectX 10-compatible graphics card
DXVA 1.0	Windows XP, Windows Server 2003	DirectX 9.0c-compatible graphics card

Happy coding, and remember: with great power comes great responsibility (to optimize your video playback experiences)!

Frequently Asked Question

Decoding and scaling NV12 surfaces can be a challenge. But fear not, dear developers, for we have some answers to get you unstuck!