05_jpeg_encode

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

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Overview

This sample demonstrates how to:

• Use the libv4l2 conversion component function to allocate buffer
• Set up attributes
• Use the JPEG encode component to encode YUV data to a file.

This sample does not require a camera.

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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/05_jpeg_encode
   $ make
  

To run

• Enter:

   $ ./jpeg_encode <in-file> <in-width> <in-height> <out-file> [OPTIONS]
  

Example

   $ ./jpeg_encode ../../data/Picture/nvidia-logo.yuv 1920 1080 test.jpg

Note

The jpeg_encode sample consumes a YUV file. If you do not already have a YUV file, you can use the jpeg_decode sample to generate one. For example:

 $ cd $HOME/tegra_multimedia_api/samples/06_jpeg_decode/
 $ ./jpeg_decode num_files 1 ../../data/Picture/nvidia-logo.jpg ../../data/Picture/nvidia-logo.yuv

Flow

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

Additional Details

The output plane is used to receive input and the capture plane is used to produce output. The YUV data format prior to entering the JPEG encoder can be block, linear, or pitch linear. This results in 2 different encode processes: encodeFromFD and encodeFromBuffer. encodeFromFD allows JPEG encode hardware to process the data directly. encodeFromBuffer requires extra format conversion prior to writing to the JPEG file.

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Key Structure and Classes

The struct context_t global structure manages all of the resources in the application.

NvVideoDecoder	Description
class NvVideoConverter	Contains elements and functions regarding video format conversion.
class NvJpegEncoder	Contains elements and functions to encode JPEG images.

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

NvVideoConverter Member	Description
output_plane	V4l2 output plane.
capture_plane	V4l2 capture plane.
waitForIdle	Wait until all queued output plane buffers are processed and dequeued from the capture plane.
setOutputPlaneFormat	Set output plane format.
setCapturePlaneFormat	Set capture plane format.

The NvVideoConverter elements output_plane and capture_plane belong to the NvV4l2ElementPlane class. Key members of NvV4l2ElementPlane used in the sample are as follows:

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 the dqueue buffer thread.
startDQThread	Start the thread of the dqueue buffer.
stopDQThread	Stop the thread of the dqueue buffer.
qBuffer	Queue the V4l2 buffer.
dqBuffer	Dequeue the V4l2 buffer.
getNumBuffers	Get the number of the V4l2 buffer.
getNumQueuedBuffers	Get the number of the V4l2 buffer under queue.
getNthBuffer	Get the NvBuffer at Index N.

The NvJpegEncoder class contains all of the functions for JPEG encoding. Key members used are:

NvV4l2ElementPlane	Description
encodeFromFd	Encode from FD of buffer exported by V4L2 element.
encodeFromBuffer	Encode from pointers of buffer data.