Overview
The JPEG decode sample demonstrates JPEG decode and optional use of the lib4L2 conversion API, should buffer format conversion be required.
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 /usr/src/jetson_multimedia_api/samples/06_jpeg_decode $ make
To run
- Enter:
$ ./jpeg_decode num_files <number of files to decode> \ <in-file1> <out-file1> ...<in-filen> <out-filen> [OPTIONS]
Example
$ ./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 the sample.
Additional Details
The output plane is used to receive input and the capture plane is used to produce output. When calling decodeToFd, the data format matches Tegra hardware so that no format conversion is required. Calling decodeToBuffer requires converting the buffer to software format after hardware-accelerated JPEG decoding. The JPEG file format contains the standard software format.
Key Structure and Classes
This sample uses the following key structures and classes:
| Element | Description |
|---|---|
| NvVideoConverter | Contains elements and functions for video format conversion. |
| NvJpegDecoder | Contains elements and functions for decoding 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 NvJpegDecoder class contains all of the functions for JPEG image decoding. Key members used are:
| Function | Description |
|---|---|
| decodeToFd | Decode to hardware buffer (at a file descriptor) where the data is available to other components. |
| decodeToBuffer | Decode to a software buffer. |