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• libav how to change stream codec

  9 novembre 2018, par Rodolfo Picoreti

  I am trying to reproduce with libav the same thing that the following ffmpeg command does :

  ffmpeg -f v4l2 -framerate 25 -video_size 640x480 -i /dev/video 0 -f
  mpegts -codec:v mpeg1video -s 640x480 -b:v 1000k -bf 0 -muxdelay
  0.001 http://localhost:8081/supersecret

  I manage to reproduce most part of it. The problem is that when allocating the "mpegts" stream (line 23) the codec that is selected is "mpeg2video", but I need it to be "mpeg1video". I tried forcing the codec_id variable to be "mpeg1video" (line 25) and it kinda worked, although I get a lot of artifacts in the image so I am guessing this is not how you do it. How can I properly change the codec in this case (that is, the "-codec:v mpeg1video" part of the ffmpeg command) ?

  C++ code being used :

  #include <exception>
  
  #include <opencv2></opencv2>core.hpp>
  
  #include <opencv2></opencv2>highgui.hpp>
  
  #include <opencv2></opencv2>imgproc.hpp>
  
  
  
  extern "C" {
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>error.h>
  
  #include <libavutil></libavutil>frame.h>
  
  #include <libavutil></libavutil>imgutils.h>
  
  }
  
  
  
  struct AVStreamer {
  
    AVFormatContext* format_context;
  
    AVStream* stream;
  
    AVCodecContext* codec_context;
  
    AVCodec* codec;
  
    AVFrame* frame;
  
    int64_t next_pts;
  
  
  
    void init_format_context(const char* url) {
  
      avformat_alloc_output_context2(&amp;format_context, nullptr, "mpegts", url);
  
      if (format_context == nullptr) throw std::runtime_error("Could not create output context");
  
      format_context->oformat->video_codec = AV_CODEC_ID_MPEG1VIDEO;
  
    }
  
  
  
    void init_codec() {
  
      auto codec_id = format_context->oformat->video_codec;
  
      codec = avcodec_find_encoder(codec_id);
  
      if (codec == nullptr) throw std::runtime_error("Could not find encoder");
  
    }
  
  
  
    void init_stream() {
  
      stream = avformat_new_stream(format_context, nullptr);
  
      if (stream == nullptr) throw std::runtime_error("Failed to alloc stream");
  
      stream->id = format_context->nb_streams - 1;
  
    }
  
  
  
    void init_codec_context() {
  
      codec_context = avcodec_alloc_context3(codec);
  
      if (codec_context == nullptr) throw std::runtime_error("Failed to alloc encoding context");
  
  
  
      auto codec_id = format_context->oformat->video_codec;
  
      codec_context->codec_id = codec_id;
  
      codec_context->bit_rate = 400000;
  
      codec_context->width = 640;
  
      codec_context->height = 480;
  
      stream->time_base = AVRational{1, 30};
  
      codec_context->time_base = stream->time_base;
  
      codec_context->gop_size = 30;  // one intra frame every gop_size
  
      // codec_context->max_b_frames = 0;  // output delayed by max_b_frames
  
      codec_context->pix_fmt = AV_PIX_FMT_YUV420P;
  
      if (codec_context->codec_id == AV_CODEC_ID_MPEG1VIDEO) { codec_context->mb_decision = 2; }
  
      if (format_context->oformat->flags &amp; AVFMT_GLOBALHEADER) {
  
        codec_context->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
    }
  
  
  
    void init_frame() {
  
      frame = av_frame_alloc();
  
      if (frame == nullptr) throw std::runtime_error("Failed to alloc frame");
  
      frame->format = codec_context->pix_fmt;
  
      frame->width = codec_context->width;
  
      frame->height = codec_context->height;
  
  
  
      auto status = av_frame_get_buffer(frame, 32);
  
      if (status &lt; 0) { throw std::runtime_error("Could not allocate frame data.\n"); }
  
    }
  
  
  
    void open_stream(const char* url) {
  
      int status = avcodec_open2(codec_context, codec, nullptr);
  
      if (status != 0) throw std::runtime_error("Failed to open codec");
  
  
  
      // copy the stream parameters to the muxer
  
      status = avcodec_parameters_from_context(stream->codecpar, codec_context);
  
      if (status &lt; 0) throw std::runtime_error("Could not copy the stream parameters");
  
  
  
      av_dump_format(format_context, 0, url, 1);
  
  
  
      if (!(format_context->oformat->flags &amp; AVFMT_NOFILE)) {
  
        status = avio_open(&amp;format_context->pb, url, AVIO_FLAG_WRITE);
  
        if (status &lt; 0) throw std::runtime_error("Could not open output file");
  
      }
  
  
  
      // Write the stream header, if any.
  
      status = avformat_write_header(format_context, nullptr);
  
      if (status &lt; 0) throw std::runtime_error("Error occurred when opening output file");
  
    }
  
  
  
    AVStreamer(const char* url) : next_pts(0) {
  
      init_format_context(url);
  
      init_codec();
  
      init_stream();
  
      init_codec_context();
  
      init_frame();
  
      open_stream(url);
  
    }
  
  
  
    virtual ~AVStreamer() {
  
      avformat_free_context(format_context);
  
      avcodec_free_context(&amp;codec_context);
  
      av_frame_free(&amp;frame);
  
    }
  
  
  
    void send(cv::Mat const&amp; image) {
  
      cv::cvtColor(image, image, CV_BGR2YUV);
  
      cv::Mat planes[3];
  
      cv::split(image, planes);
  
      cv::pyrDown(planes[1], planes[1]);
  
      cv::pyrDown(planes[2], planes[2]);
  
  
  
      if (av_frame_make_writable(frame) &lt; 0) {
  
        throw std::runtime_error("Failed to make frame writable");
  
      }
  
  
  
      frame->data[0] = planes[0].data;
  
      frame->linesize[0] = planes[0].step;
  
      frame->data[1] = planes[1].data;
  
      frame->linesize[1] = planes[1].step;
  
      frame->data[2] = planes[2].data;
  
      frame->linesize[2] = planes[2].step;
  
      frame->pts = next_pts++;
  
  
  
      AVPacket packet;
  
      av_init_packet(&amp;packet);
  
  
  
      int status = avcodec_send_frame(codec_context, frame);
  
      if (status &lt; 0) throw std::runtime_error("Send frame failed");
  
  
  
      status = avcodec_receive_packet(codec_context, &amp;packet);
  
      if (status == AVERROR(EAGAIN)) { return; }
  
      if (status &lt; 0) throw std::runtime_error("Receive packet failed");
  
  
  
      av_packet_rescale_ts(&amp;packet, codec_context->time_base, stream->time_base);
  
      packet.stream_index = stream->index;
  
      av_interleaved_write_frame(format_context, &amp;packet);
  
    }
  
  };
  
  
  
  int main(int argc, char** argv) {
  
    av_register_all();
  
    avformat_network_init();
  
  
  
    auto url = argc == 2 ? argv[1] : "http://localhost:8081/supersecret";
  
    AVStreamer streamer(url);
  
  
  
    cv::VideoCapture video(0);
  
    assert(video.isOpened() &amp;&amp; "Failed to open video");
  
  
  
    for (;;) {
  
      cv::Mat image;
  
      video >> image;
  
      streamer.send(image);
  
    }
  
  }
  
  </exception>

• Create movie programatically with ffmpeg

  16 janvier 2019, par Martin Delille

  I would like to create a movie programatically with ffmpeg.

  Here is my code :

  QString fileName = "test.mov";
  
  static char errorString[AV_ERROR_MAX_STRING_SIZE];
  
  
  
  printf("Video encoding\n");
  
  
  
  AVOutputFormat *outputFormat = av_guess_format(nullptr, fileName.toStdString().c_str(), nullptr);
  
  
  
  if (outputFormat == nullptr) {
  
      qDebug() << "Could not find suitable format for" << fileName;
  
      return false;
  
  }
  
  
  
  enum AVCodecID codec_id = AV_CODEC_ID_MJPEG;
  
  
  
  qDebug() << "Format Name:" << outputFormat->name;
  
  qDebug() << "Format Video Codec:" << outputFormat->video_codec;
  
  outputFormat->video_codec = codec_id;
  
  
  
  /// allocate the output media context, formatContext
  
  AVFormatContext *formatContext = avformat_alloc_context();
  
  formatContext->oformat = outputFormat;
  
  
  
  // find the mpeg1 video encoder
  
  AVCodec *codec = avcodec_find_encoder(codec_id);
  
  
  
  if (!codec) {
  
      qDebug() << "codec not found";
  
      return false;
  
  }
  
  
  
  qDebug() << "Codec name:" << codec->name;
  
  
  
  AVStream *videoStream = avformat_new_stream(formatContext, codec);
  
  // put sample parameters
  
  videoStream->codecpar->bit_rate = 400000;
  
  videoStream->codecpar->width = width;
  
  videoStream->codecpar->height = height;
  
  videoStream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
  
  videoStream->codecpar->format = AV_PIX_FMT_YUVJ422P;
  
  videoStream->time_base.num = 1;
  
  videoStream->time_base.den = 25;
  
  
  
  AVCodecContext *codecContext = avcodec_alloc_context3(nullptr);
  
  codecContext->codec_id = codec_id;
  
  codecContext->codec_type = AVMEDIA_TYPE_VIDEO;
  
  codecContext->width = width;
  
  codecContext->height = height;
  
  codecContext->time_base.num = 1;
  
  codecContext->time_base.den = 25;
  
  codecContext->pix_fmt = AV_PIX_FMT_YUVJ422P;
  
  
  
  if (int error = avcodec_parameters_to_context(codecContext, videoStream->codecpar)) {
  
      qDebug() << "Error parameting the context:" << av_make_error_string(errorString, AV_ERROR_MAX_STRING_SIZE, error);
  
      return false;
  
  }
  
  
  
  // open it
  
  if (int error = avcodec_open2(codecContext, codec, nullptr)) {
  
      qDebug() << "Could not open codec:" << av_make_error_string(errorString, AV_ERROR_MAX_STRING_SIZE, error);
  
      return false;
  
  }
  
  
  
  // alloc image and output buffer
  
  AVFrame *frame = av_frame_alloc();
  
  frame->format = codecContext->pix_fmt;
  
  frame->width = codecContext->width;
  
  frame->height = codecContext->height;
  
  
  
  if (int error = av_image_alloc(frame->data, frame->linesize, frame->width, frame->height, static_cast<enum avpixelformat="avpixelformat">(frame->format), 0)) {
  
      qDebug() &lt;&lt; "Error allocating image data:" &lt;&lt; av_make_error_string(errorString, AV_ERROR_MAX_STRING_SIZE, error);
  
      return false;
  
  }
  
  
  
  // Open the output file, if needed
  
  if (!(outputFormat->flags &amp; AVFMT_NOFILE)) {
  
      if (avio_open(&amp;formatContext->pb, fileName.toStdString().c_str(), AVIO_FLAG_WRITE) &lt; 0) {
  
          qDebug() &lt;&lt; "Could not open" &lt;&lt; fileName;
  
          return false;
  
      }
  
  }
  
  
  
  // some formats want stream headers to be separate
  
  if (formatContext->oformat->flags &amp; AVFMT_GLOBALHEADER) {
  
      codecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
  }
  
  
  
  if (int error = avformat_write_header(formatContext, nullptr)) {
  
      qDebug() &lt;&lt; "error writing header:" &lt;&lt; av_make_error_string(errorString, AV_ERROR_MAX_STRING_SIZE, error);
  
      return false;
  
  }
  
  </enum>

  Unfortunately, when I execute it I have the following output :

  Format Name: mov
  
  Format Video Codec: 27
  
  Codec name: mjpeg
  
  [mov @ 0x1048c7000] Could not find tag for codec none in stream #0, codec not currently supported in container
  
  error writing header: Invalid argument

  What am I doing wrong ?

• Live555 truncates encoded data of FFMpeg

  22 novembre 2019, par Harshil Makwana

  I am trying to stream H264 based data using Live555 over RTSP.

  I am capturing data using V4L2, and then encodes it using FFMPEG and then passing data to Live555’s DeviceSource file, in that I using H264VideoStreamFramer class,

  Below is my codec settings to configure AVCodecContext of encoder,

  codec = avcodec_find_encoder_by_name(CODEC_NAME);
  
  if (!codec) {
  
      cerr << "Codec " << codec_name << " not found\n";
  
      exit(1);
  
  }
  
  
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      cerr << "Could not allocate video codec context\n";
  
      exit(1);
  
  }
  
  
  
  pkt = av_packet_alloc();
  
  if (!pkt)
  
      exit(1);
  
  
  
  /* put sample parameters */
  
  c->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  c->width = PIC_HEIGHT;
  
  c->height = PIC_WIDTH;
  
  /* frames per second */
  
  c->time_base = (AVRational){1, FPS};
  
  c->framerate = (AVRational){FPS, 1};
  
  c->gop_size = 10;
  
  c->max_b_frames = 1;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  c->rtp_payload_size = 30000;
  
  if (codec->id == AV_CODEC_ID_H264)
  
      av_opt_set(c->priv_data, "preset", "fast", 0);
  
  av_opt_set_int(c->priv_data, "slice-max-size", 30000, 0);
  
  /* open it */
  
  ret = avcodec_open2(c, codec, NULL);
  
  if (ret < 0) {
  
      cerr << "Could not open codec\n";
  
      exit(1);
  
  }

  And I am getting encoded data using avcodec_receive_packet() function. which will return AVPacket.

  And I am passing AVPacket’s data into DeviceSource file below is code snippet of my Live555 code :

  void DeviceSource::deliverFrame() {
  
      if (!isCurrentlyAwaitingData()) return; // we're not ready for the data yet
  
  
  
      u_int8_t* newFrameDataStart = (u_int8_t*) pkt->data;
  
      unsigned newFrameSize = pkt->size; //%%% TO BE WRITTEN %%%
  
      // Deliver the data here:
  
      if (newFrameSize > fMaxSize) { // Condition becomes true many times
  
          fFrameSize = fMaxSize;
  
          fNumTruncatedBytes = newFrameSize - fMaxSize;
  
      } else {
  
          fFrameSize = newFrameSize;
  
      }
  
      gettimeofday(&fPresentationTime, NULL); // If you have a more accurate time - e.g., from an encoder - then use that instead.
  
      // If the device is *not* a 'live source' (e.g., it comes instead from a file or buffer), then set "fDurationInMicroseconds" here.
  
      memmove(fTo, newFrameDataStart, fFrameSize);
  
  }

  But here, sometimes my packet’s size is getting more than fMaxSize value and as per LIVE555 logic it will truncate frame data, so that sometimes I am getting bad frames on my VLC,

  From Live555 forum, I get to know that encoder should not send packet whose size is more than fMaxSize value, so my question is :

  How to restrict encoder to limit size of packet ?

  Thanks in Advance,

  Harshil