02_video_dec_cuda

• Overview
• Building and Running
• Flow
• Key Structure and Classes

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Overview

This sample demonstrates how the buffer allocated by the libv4l2 component is used to decode H.265/H.264 video streams, and how CUDA is used aid in rendering images without extra memory copy operations.

Supported video formats:

• H.264
• H.265

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Building and Running

Prerequisites

• You have followed Steps 1-3 in Building and Running.
• If you are building from your host Linux PC (x86), you have followed Step 4 in Building and Running.

To build:

• Enter:

   $ cd $HOME/tegra_multimedia_api/samples/02_video_dec_cuda
   $ make
  

To run

• Enter:

   $ ./video_dec_cuda <in-file> <in-format> [options]
  

Example

   $ ./video_dec_cuda ../../data/Video/sample_outdoor_car_1080p_10fps.h264 H264

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Flow

The following diagram shows the flow of data through the sample.

Additional Details

The main flow of this sample is as follows:

Tegra provides pitch linear and block linear memory format support on input and output. Input and output memory formats do not need to match.

    ret = ctx->conv->setOutputPlaneFormat(format.fmt.pix_mp.pixelformat,
                                              format.fmt.pix_mp.width,
                                              format.fmt.pix_mp.height,
                                              NvVideoConverter::LAYOUT_BLOCK);

This call sets up libv4l2 output plane, i.e., for receiving input as YUV data for decoder, in block linear format. This is the format that complies with Tegra hardware.

    ret = ctx->conv->setCapturePlaneFormat(format.fmt.pix_mp.pixelformat,
                                               format.fmt.pix_mp.width,
                                               format.fmt.pix_mp.height,
                                               NvVideoConverter::LAYOUT_PITCH);

This call sets up the libv4l2 capture plane in pitch linear format. This is the format that is common to the software implementation.

NvEGLImageFromFd is syntax error that returns an EGLImage pointer from file descriptor buffer that is allocated by by the member function of NvVideoDecoder base class. An EGLImage buffer is then used by CUDA to render a black box on the display. This is implemented in a separate common routine using EGLImage.

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Key Structure and Classes

This sample uses the following key structures and classes:

Element	Description
NvVideoDecoder	Contains all video decoding-related elements and functions.
NvVideoConverter	Contains elements and functions for video format conversion.
NvEglRenderer	Contains all EGL display rendering-related functions.
egl_image	The EGLImage used for CUDA processing.
conv_output_plane_buf_queue	Output plane queue for video conversion.
dec_capture_loop	The thread handler for decoding capture loop.

NvVideoDecoder packages all video decoding-related elements and functions. Key members used in the sample are:

Member	Description
output_plane	V4l2 output plane.
capture_plane	V4l2 capture plane.
createVideoDecoder	Static function to create video decode object.
subscribeEvent	Subscribe event.
setExtControls	Set external control to V4l2 device.
setOutputPlaneFormat	Set output plane format.
setCapturePlaneFormat	Set capture plane format.
getControl	TBD
dqEvent	Dqueue the event which report by V4l2 device.
isInError	Check if under error state.

NvVideoConverter packages all video converting-related elements and functions. Key members used in the sample are:

Member	Description
output_plane	The output plane.
capture_plane	The capture plane.
waitForIdle	TBD
setOutputPlaneFormat	Set output plane format.
setCapturePlaneFormat	Set capture plane format.

Both NvVideoDecoder and NvVideoConverter contain 2 key elements: output_plane and capture_plane. These 2 objects belong to the same class type NvV4l2ElementPlane. Key members used in the sample are:

Element	Description
setupPlane	Setup the plane of V4l2 element.
deinitPlane	Destroy the plane of V4l2 element.
setStreamStatus	Start/Stop the stream.
setDQThreadCallback	Set the callback function of dqueue buffer thread.
startDQThread	Start the thread of dqueue buffer.
stopDQThread	Stop the thread of dqueue buffer.
qBuffer	Queue V4l2 buffer.
dqBuffer	Dqueue V4l2 buffer.
getNumBuffers	Get the number of V4l2 buffer.
getNumQueuedBuffers	Get the number of V4l2 buffer which under queue.
getNthBuffer	TBD

Two global functions are used to create and destroy EGLImage from the dmabuf file descriptor:

Function	Description
NvEGLImageFromFd	Create EGLImage from dmabuf file descriptor.
NvDestroyEGLImage	Destroy the EGLImage.