How to create grayscale video with avconv? - c++

Question

I've been looking for some time for a quick and reliable way of creating grayscale videos with avconv library from frames that are captured/created with OpenCV, in a C++ application.
I know that OpenCV have it's internal way of creating videos, however, it has some encoding performance and options limitations.
So, in this way, I would like to know which are the options for accomplishing this task?

Answer 1

For accomplishing this task, one of the options that I've found, which complies with my needs is the following class:
extern "C" {
#include <libavcodec/avcodec.h>
#include <libavutil/mathematics.h>
}
class AVConvVideoMaker
{
AVCodec* codec;
AVCodecContext* context;
AVFrame* picture;
int imgWidth, imgHeight, imgBufferSize;
FILE* outputFile;
int outputBufferSize;
uint8_t* outputBuffer;
int pictureBufferSize;
uint8_t* pictureBuffer;
int outputSize;
public:
AVConvVideoMaker(std::string outputFilePath, int imgWidth, int imgHeight)
: codec(NULL)
, context(NULL)
, picture(NULL)
, imgWidth(imgWidth)
, imgHeight(imgHeight)
, imgBufferSize(imgWidth*imgHeight)
, outputFile(fopen(outputFilePath.c_str(), "wb"))
, outputBufferSize(100000)
, outputBuffer(new uint8_t[outputBufferSize])
, pictureBufferSize((imgBufferSize*3)/2)
, pictureBuffer(new uint8_t[pictureBufferSize])
, outputSize(0)
{
avcodec_register_all();
this->codec = avcodec_find_encoder(CODEC_ID_MPEG1VIDEO);
if (!this->codec)
{
throw std::runtime_error("Codec not found");
}
this->context = avcodec_alloc_context3(codec);
this->picture = avcodec_alloc_frame();
this->context->bit_rate = 400000;
this->context->width = this->imgWidth;
this->context->height = this->imgHeight;
this->context->time_base = (AVRational){1, 25};
this->context->gop_size = 10;
this->context->max_b_frames = 1;
this->context->pix_fmt = PIX_FMT_YUV420P;
if(avcodec_open2(this->context, this->codec, NULL) < 0)
{
throw std::runtime_error("Could not open codec");
}
if(!this->outputFile)
{
throw std::runtime_error("Could not open video output file");
}
this->picture->data[0] = this->pictureBuffer;
this->picture->data[1] = this->picture->data[0] + imgBufferSize;
this->picture->data[2] = this->picture->data[1] + imgBufferSize / 4;
this->picture->linesize[0] = this->imgWidth;
this->picture->linesize[1] = this->imgWidth / 2;
this->picture->linesize[2] = this->imgWidth / 2;
}
void insertFrame(cv::Mat1b& img)
{
fflush(stdout);
/* Y */
for(int y=0; y < this->context->height; y++)
{
for(int x=0; x < this->context->width; x++)
{
this->picture->data[0][y * picture->linesize[0] + x] = img.at<uchar>(y,x);
}
}
/* Cb and Cr */
for(int y=0; y < this->context->height/2; y++)
{
for(int x=0; x < this->context->width/2; x++)
{
this->picture->data[1][y * this->picture->linesize[1] + x] = 128;
this->picture->data[2][y * this->picture->linesize[2] + x] = 128;
}
}
this->outputSize = avcodec_encode_video(this->context, this->outputBuffer, this->outputBufferSize, this->picture);
fwrite(this->outputBuffer, 1, outputSize, this->outputFile);
}
~AVConvVideoMaker()
{
this->outputBuffer[0] = 0x00;
this->outputBuffer[1] = 0x00;
this->outputBuffer[2] = 0x01;
this->outputBuffer[3] = 0xb7;
fwrite(this->outputBuffer, 1, 4, this->outputFile);
fclose(this->outputFile);
avcodec_close(this->context);
av_free(this->context);
av_free(this->picture);
delete outputBuffer;
delete pictureBuffer;
}
};
For compiling this in Ubuntu 16.04, you have to link with:
g++ --std=c++11 main.cpp -lopencv_core -lopencv_highgui -lavutil -lavcodec