extract_subs.cpp

#include <iostream>
#include <fstream>
#include <sstream>

extern "C" {
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/timestamp.h>
}

using namespace std;

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

    if (argc != 2) {
        cerr << "Usage: " << argv[0] << " <input_file>" << endl;
        return 1;
    }

    const char* input_file = argv[1];

    avformat_network_init();

    AVFormatContext* format_context = nullptr;
    int error = avformat_open_input(&format_context, input_file, nullptr, nullptr);
    if (error != 0) {
        cerr << "Failed to open input file" << endl;
        return 1;
    }

    error = avformat_find_stream_info(format_context, nullptr);
    if (error < 0) {
        cerr << "Failed to find stream information" << endl;
        return 1;
    }

    const AVCodec* codec = nullptr;
    AVCodecParameters* codec_parameters = nullptr;
    int stream_index = av_find_best_stream(format_context, AVMEDIA_TYPE_SUBTITLE, -1, -1, &codec, 0);
    if (stream_index < 0) {
        cerr << "Failed to find subtitle stream in input file" << endl;
        return 1;
    }

    codec_parameters = format_context->streams[stream_index]->codecpar;
    AVCodecContext* codec_context = avcodec_alloc_context3(codec);
    if (!codec_context) {
        cerr << "Failed to allocate codec context" << endl;
        return 1;
    }

    error = avcodec_parameters_to_context(codec_context, codec_parameters);
    if (error < 0) {
        cerr << "Failed to copy codec parameters to codec context" << endl;
        return 1;
    }

    error = avcodec_open2(codec_context, codec, nullptr);
    if (error < 0) {
        cerr << "Failed to open codec" << endl;
        return 1;
    }

    AVPacket packet;
    av_init_packet(&packet);

    while (av_read_frame(format_context, &packet) >= 0) {
        if (packet.stream_index == stream_index) {
            AVSubtitle subtitle;
            int got_subtitle;
            error = avcodec_decode_subtitle2(codec_context, &subtitle, &got_subtitle, &packet);
            if (error < 0) {
                cerr << "Failed to decode subtitle" << endl;
            }
            if (got_subtitle) {
                for (unsigned int i = 0; i < subtitle.num_rects; ++i) {
                    AVSubtitleRect* rect = subtitle.rects[i];
                    if (rect->type == SUBTITLE_ASS) {
                        std::cout << rect->ass;
                    }else if (rect->type == SUBTITLE_TEXT){
                        std::cout << "!" << rect->text;
                    }
                }
                avsubtitle_free(&subtitle);
            }
        }
        av_packet_unref(&packet);
    }

    avformat_network_deinit();

}