OpenCV checking if video-codec is installed on machine (C++)

Question

Problem:

I want to implement a safe version to process data into a video via OpenCV, this should work on Windows, Mac and Linux. The data has to be saved in a lossless video-codec.

Saving the file under my current setup is no problem at all, and I know that using -1 as fourcc with videoWriter will pop up a window. What I can't assure is that the system has the ability to show a window at all! So the popup-menu is okay as fallback, but not as the main solution.

Question:

Is there a way to check with OpenCV if a specific video-codec is installed on the machine without running into compile problems? Something like:

if (`codec installed`)
    int codec = opencvfourcc(codec)
else
    int codec = -1

What exactly `int codec = opencvfourcc(codec)` is suposed to do? Can you show some real code? — n. m. could be an AI, Jun 20 '18 at 14:09
@GPPK Could you please explain your reaction. I already read it and ensured to mention in the question, that this won't help. — Patrick Abraham, Jun 20 '18 at 15:17
@n.m. OpenCV works internally mostly on integer flags, opencvfourcc is actually `cv::VideoWriter::fourcc` and is a defined function, taking in 4 chars and returns an integer. So it's already defined ^^. — Patrick Abraham, Jun 20 '18 at 15:21
*OpenCV works* Well, having read the description of the API, I strongly disagree with this statement (at least as far as writing video files is concerned). — n. m. could be an AI, Jun 20 '18 at 15:57
Let's restate that, most important flags, like codecs, modes or types are all handled with integers in OpenCV. — Patrick Abraham, Jun 20 '18 at 23:08

zindarod · Accepted Answer · 2018-06-20T15:06:15.917

OpenCV uses FFmpeg to decode video files. So if OpenCV has been built with the version of FFmpeg on the system, then we can use the FFmpeg command line to check for availability of our codec of choice. To run system commands from C++, I've used code from here. This post details how to check for OS type.

#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>

#if defined(_WIN32) || defined(_WIN64)
#define OS_WINDOWS
#elif defined(__APPLE__) || defined(__MACH__)
#define OS_OSX
#elif defined(__linux__)
#define OS_LINUX
#endif

std::string exec(const std::string& command ) {
    const char* cmd = command.c_str();
    std::array<char, 128> buffer;
    std::string result;

    #if defined(OS_WINDOWS)
    std::shared_ptr<FILE> pipe(_popen(cmd, "r"), _pclose);
    #elif defined(OS_LINUX) || defined (OS_OSX)
    std::shared_ptr<FILE> pipe(popen(cmd, "r"), pclose);
    #endif

    if (!pipe) throw std::runtime_error("popen() failed!");
    while (!feof(pipe.get())) {
        if (fgets(buffer.data(), 128, pipe.get()) != nullptr)
            result += buffer.data();
    }
    return result;
}

int main() {

  // codec of choice
  std::string codec = "H264";

  // if OS is linux or OSX then use FFmpeg with grep command
  #if defined (OS_LINUX) || defined (OS_OSX)
  std::string command = "ffmpeg -codecs | grep -i ";
  // if WINDOWS then FFmpeg with findstr
  #elif defined (OS_WINDOWS)
  std::string command = "ffmpeg -codecs | findstr /i ";
  #endif

  // execute the system command and get the output
  std::string str = exec(command+codec);

  // if the output string contains the letters DEV then FFmpeg supports the codec
  // D: Decoding supported
  // E: Encoding supported
  // V: Video codec
  std::size_t found = str.find("DEV");

  if(found != std::string::npos)
    std::cout<<"Codec Found"<<std::endl;

return 0;
}

Nice workaround, isn't the most beautiful solution, but it's none the less really helpful. Will wait a few hours before I accept the answer. — Patrick Abraham, Jun 20 '18 at 15:31
@PatrickAbraham You can use FFmpeg to get codec & container availability. Just as OpenCV does [here](https://github.com/opencv/opencv/blob/3.4/modules/videoio/src/cap_ffmpeg_impl.hpp#L1966) and [here](https://github.com/opencv/opencv/blob/3.4/modules/videoio/src/cap_ffmpeg_impl.hpp#L1993). — zindarod, Jun 20 '18 at 21:08

OpenCV checking if video-codec is installed on machine (C++)

1 Answers1