16_multivideo_encode (multi video transcode)

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

---

Overview

The multivideo_transcode sample program demonstrates how to transcode multiple video streams in parallel.

The application reads input buffers from a bitstream file, performs decoding, and generates a YUV file, it passes the YUV file to the encoder to encode it back to the desired codec format. It can do transcoding for multipe input streams and generate multiple output, each independent of other.

The application runs on file source simulated input buffers, and so does not require a camera.

Supported video formats are:

• H.264
• H.265
• VP8
• VP9

---

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/16_multivideo_transcode
   $ make
  

To run

• Enter:

  $ ./multivideo_transcode num_files <number_of_files> <in-file1> <in-pixfmt1> <out-file1> <out-pixfmt1> <in-file2> <in-pixfmt2> <out-file2> <out-pixfmt2> ... [OPTIONS]
  

To view supported options

Enter:

   $ ./multivideo_transcode --help

Example

   $ ./multivideo_transcode num_files 2 ../../data/Video/sample_outdoor_car_1080p_10fps.h264 H264 sample_outdoor_car_1080p_10fps.h265 H265 ../../data/Video/sample_outdoor_car_1080p_10fps.h264 H264 sample_outdoor_car_1080p_10fps_second.vp9 VP9

---

Flow

The following diagram shows the flow through this sample.

1. The Output Plane of the Decoder receives input in bitstream format and delivers it to the Decoder for decoding.
2. The Capture Plane of the Decoder transfers decoded YUV frames to the Output Plane of the Encoder to encode.
3. The Capture Plane of the Encoder transfers encoded frames to the application in bitstream format.
4. The encoded bitstream is written to a file.
5. For the Decoder the application supports MMAP at Output Plane and DMABUF at Capture Plane.
6. For the Encoder the application supports DMABUF at Output Plane and MMAP at Capture Plane.

---

Key Structure and Classes

The sample uses the following key structures and classes.

Element	Description
NvVideoEncoder	Contains all video encoding-related elements and functions.
NvVideoDecoder	Contains all video decoding-related elements and functions.
encoder_capture_plane_dq_callback	A pointer to the thread handler for the encoding capture loop.
dec_capture_loop	A pointer to the thread handler for the decoding capture loop as well as encoding output loop.

The NvVideoEncoder class and the NvVideoDecoder class packages all video encoding and decoding related elements and functions. Key members used in the sample are:

Member	Description
output_plane	Specifies the V4L2 output plane.
capture_plane	Specifies the V4L2 capture plane.
createVideoDecoder	Static function to create video decode object.
createVideoEncoder	Static function to create video encode object.
subscribeEvent	Subscribes to event.
setOutputPlaneFormat	Set output plane format.
setCapturePlaneFormat	Set capture plane format.
dqEvent	Dequeues the event reported by the V4L2 device.
isInError	Checks if under error state.

Classes NvVideoEncoder and NvVideoDecoder contain two key elements each: output_plane and capture_plane. These objects are derived from class type NvV4l2ElementPlane. The sample uses the following key members:

Element	Description
setupPlane	Sets up the plane of V4L2 element.
deinitPlane	Destroys the plane of the V4L2 element.
setStreamStatus	Starts/stops the stream.
setDQThreadCallback	Sets the callback function of the dqueue buffer thread.
startDQThread	Starts the thread of the dqueue buffer.
stopDQThread	Stops the thread of the dqueue buffer.
qBuffer	Queues the V4L2 buffer.
dqBuffer	Dequeues the V4L2 buffer.
getNumBuffers	Gets the number of V4L2 buffers.
getNumQueuedBuffers	Gets the number of buffers currently queued on the plane.