mosh-me/app/mosh-me.cpp

extern "C" {
#include <libavformat/avformat.h>
#include <libavutil/error.h>
}

#include <spdlog/spdlog.h>

static void log_err(int err) {
  char buf[256];
  av_strerror(err, buf, sizeof(buf));
  spdlog::error("FFMPEG error: {}", buf);
}

static void smearStreams(const std::vector<off_t> &stream_list,
                         AVFormatContext *input_format,
                         AVFormatContext *output_format) {

  bool remove_iframes = false;

  AVPacket prev;
  for (;;) {
    AVPacket packet;
    if (auto ret = av_read_frame(input_format, &packet); ret < 0) {
      break;
    }

    AVStream *istream = input_format->streams[packet.stream_index];
    if (packet.stream_index >= input_format->nb_streams ||
        stream_list[packet.stream_index] < 0 ||
        (istream->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
         packet.flags & AV_PKT_FLAG_KEY && remove_iframes)) {
      av_packet_unref(&packet);
      continue;
    }

    // Map to output stream index
    packet.stream_index = stream_list[packet.stream_index];
    AVStream *ostream = output_format->streams[packet.stream_index];

    if (packet.pts > 0 && packet.pts % 25 < 10 && packet.pts % 2 == 0) {
      prev.pts = packet.pts;
      prev.dts = packet.dts;
      prev.duration = packet.duration;
      packet = prev;
    }

    // Adjust time data for output timebase
    packet.pts =
        av_rescale_q_rnd(packet.pts, istream->time_base, ostream->time_base,
                         AVRounding(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
    packet.dts =
        av_rescale_q_rnd(packet.dts, istream->time_base, ostream->time_base,
                         AVRounding(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
    packet.duration =
        av_rescale_q(packet.duration, istream->time_base, ostream->time_base);
    packet.pos = -1; // unknown position

    if (auto ret = av_interleaved_write_frame(output_format, &packet);
        ret < 0) {
      spdlog::error("Could not mux packet");
      log_err(ret);
    }

    prev = packet;

    av_packet_unref(&packet);
  }
  av_packet_unref(&prev);
}

static std::vector<off_t>
prepareOutputStreams(const AVFormatContext *input_format,
                     AVFormatContext *output_format) {

  std::vector<off_t> streams_list(input_format->nb_streams);
  off_t stream_ix = 0;

  for (off_t i = 0; i < input_format->nb_streams; i++) {
    AVStream *istream = input_format->streams[i];
    AVCodecParameters *icpar = istream->codecpar;
    if (icpar->codec_type != AVMEDIA_TYPE_AUDIO &&
        icpar->codec_type != AVMEDIA_TYPE_VIDEO &&
        icpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
      streams_list[i] = -1;
      continue;
    }

    streams_list[i] = stream_ix++;
    AVStream *ostream = avformat_new_stream(output_format, nullptr);
    if (auto ret = avcodec_parameters_copy(ostream->codecpar, icpar); ret < 0) {
      spdlog::error("Could not prepare output stream");
      log_err(ret);
    }
  }

  return streams_list;
}

int main(int argc, const char *argv[]) {
  if (argc < 3) {
    spdlog::error("Please invoke with {} <input file> <output file>", argv[0]);
    return 1;
  }
  spdlog::info("Opening File {}", argv[1]);

  AVFormatContext *input_format = nullptr;
  AVFormatContext *output_format = nullptr;
  if (auto ret = avformat_open_input(&input_format, argv[1], nullptr, nullptr);
      ret < 0) {
    log_err(ret);
    return 1;
  }

  if (auto ret = avformat_find_stream_info(input_format, nullptr); ret < 0) {
    log_err(ret);
  }

  spdlog::info("Format: {}, frames: {}, bitrate: {}",
               input_format->iformat->name, input_format->duration,
               input_format->bit_rate);

  if (auto ret = avformat_alloc_output_context2(&output_format, nullptr,
                                                nullptr, argv[2]);
      ret < 0) {
    log_err(ret);
  }

  auto streams = prepareOutputStreams(input_format, output_format);

  if (!(output_format->oformat->flags & AVFMT_NOFILE)) {
    if (auto ret = avio_open(&output_format->pb, argv[2], AVIO_FLAG_WRITE);
        ret < 0) {
      spdlog::error("Could not open output file {}", argv[2]);
      log_err(ret);
    }
  }

  if (auto ret = avformat_write_header(output_format, nullptr); ret < 0) {
    spdlog::error("Could not write header");
    log_err(ret);
  }

  smearStreams(streams, input_format, output_format);

  av_write_trailer(output_format);

  avformat_close_input(&input_format);
  if (output_format && !(output_format->oformat->flags & AVFMT_NOFILE)) {
    avio_closep(&output_format->pb);
  }
  avformat_free_context(output_format);
}