main.cpp

#include <iostream>
#include <memory>
#include <cstdio>
#include <string>
#include <format>
#include <cstdlib>

std::string validUsageString = "compressor <input video file> <size in mb>";

/**
 * execute a command and get the number output
 * only for windows
 * 
 * @param cmd The command to execute.
 * @return The result of the command execution as a double.
 */
double getDoubleFrom(const char* cmd) {
    std::unique_ptr<FILE, decltype(&_pclose)> pipe(_popen(cmd, "r"), &_pclose);
    double result = 0.0;
    fscanf(pipe.get(), "%lf", &result); // ignoring a lot of error handling here
    return result;
}

int main(int argc, char* argv[]) {

    std::string filename;
    double targetSize;

    if (argc != 3) {
        std::cout << "Invalid inputs" << std::endl;
        std::cout << validUsageString << std::endl;
        return 1;
    }
    
    try{
        filename = argv[1];
        targetSize = std::stod(argv[2]); // in MB
        if (targetSize <= 0) {
            std::cout << "Invalid inputs" << std::endl;
            std::cout << validUsageString << std::endl;
            return 1;
        }
    }
    catch(...){
        std::cout << "Invalid inputs" << std::endl;
        std::cout << validUsageString << std::endl;
        return 1;
    }

    double audioBitrate = getDoubleFrom(std::format("ffprobe -v error -select_streams a:0 -show_entries stream=bit_rate -of default=noprint_wrappers=1:nokey=1 \"{}\"", filename).c_str()) / 1000.0; // convert to kbps
    double fileDuration = getDoubleFrom(std::format("ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 \"{}\"", filename).c_str()); // in seconds

    double videoBitrate = ((targetSize * 8192.0) / fileDuration) - audioBitrate;

    std::system(std::format("ffmpeg -y -i \"{}\" -c:v libx264 -b:v {}k -pass 1 -an -f null -", filename, static_cast<int>(videoBitrate)).c_str());
    std::system(std::format("ffmpeg -y -i \"{}\" -c:v libx264 -b:v {}k -pass 2 -c:a aac -b:a {}k {}_compressed.mp4", filename, static_cast<int>(videoBitrate), static_cast<int>(audioBitrate), filename.substr(0, filename.find_last_of('.'))).c_str());

    std::remove("ffmpeg2pass-0.log");
    std::remove("ffmpeg2pass-0.log.mbtree");

    return 0;

}