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• Segfault while trying to fill the yuv image for rtsp streaming

  21 septembre 2016, par tankyx

  I am capturing the video stream from a window, and I want to restream it to my rtsp proxy server. However, it seems I can’t write the frame properly, but I can show the said frame in a SDL window. Here is my code :

  int StreamHandler::storeStreamData()
  
  {
  
  // Allocate video frame
  
  pFrame = av_frame_alloc();
  
  
  
  // Allocate an AVFrame structure
  
  pFrameRGB = av_frame_alloc();
  
  if (pFrameRGB == NULL)
  
      throw myExceptions("Error : Can't alloc the frame.");
  
  
  
  // Determine required buffer size and allocate buffer
  
  numBytes = avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width,
  
      pCodecCtx->height);
  
  buffer = (uint8_t *)av_malloc(numBytes * sizeof(uint8_t));
  
  
  
  // Assign appropriate parts of buffer to image planes in pFrameRGB
  
  avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_YUV420P,
  
      pCodecCtx->width, pCodecCtx->height);
  
  
  
  //InitSdlDrawBack();
  
  
  
  // initialize SWS context for software scaling
  
  
  
  sws_ctx = sws_getContext(pCodecCtx->width,
  
      pCodecCtx->height,
  
      pCodecCtx->pix_fmt,
  
      pCodecCtx->width,
  
      pCodecCtx->height,
  
      pCodecCtx->pix_fmt,
  
      SWS_LANCZOS,
  
      NULL,
  
      NULL,
  
      NULL
  
  );
  
  
  
  SetPixelArray();
  
  FfmpegEncoder enc("rtsp://127.0.0.1:1935/live/myStream");
  
  
  
  i = 0;
  
  while (av_read_frame(pFormatCtx, &packet) >= 0) {
  
      if (packet.stream_index == videoindex) {
  
          // Decode video frame
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
          if (frameFinished) {
  
              i++;
  
              //DrawFrame();
  
  
  
              sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
  
                  pFrame->linesize, 0, pCodecCtx->height,
  
                  pFrameRGB->data, pFrameRGB->linesize);
  
              enc.encodeFrame(pFrameRGB, i);
  
          }
  
      }
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&packet);
  
  }
  
  // Free the RGB image
  
  av_free(buffer);
  
  av_frame_free(&pFrameRGB);
  
  
  
  // Free the YUV frame
  
  av_frame_free(&pFrame);
  
  
  
  // Close the codecs
  
  avcodec_close(pCodecCtx);
  
  avcodec_close(pCodecCtxOrig);
  
  
  
  // Close the video file
  
  avformat_close_input(&pFormatCtx);
  
  
  
  return 0;
  
  }
  
  
  
  void StreamHandler::SetPixelArray()
  
  {
  
  yPlaneSz = pCodecCtx->width * pCodecCtx->height;
  
  uvPlaneSz = pCodecCtx->width * pCodecCtx->height / 4;
  
  yPlane = (Uint8*)malloc(yPlaneSz);
  
  uPlane = (Uint8*)malloc(uvPlaneSz);
  
  vPlane = (Uint8*)malloc(uvPlaneSz);
  
  if (!yPlane || !uPlane || !vPlane)
  
      throw myExceptions("Error : Can't create pixel array.");
  
  
  
  uvPitch = pCodecCtx->width / 2;
  
  }

  Here I fill the YUV image and write the packet.

  void FfmpegEncoder::encodeFrame(AVFrame * frame, int frameCount)
  
  {
  
  AVPacket    pkt = { 0 };
  
  int         got_pkt;
  
  
  
  av_init_packet(&pkt);
  
  frame->pts = frameCount;
  
  
  
  FillYuvImage(frame, frameCount, this->pCodecCtx->width, this->pCodecCtx->height);
  
  
  
  if (avcodec_encode_video2(this->pCodecCtx, &pkt, frame, &got_pkt) < 0)
  
      throw myExceptions("Error: failed to encode the frame. FfmpegEncoder.cpp l:61\n");
  
  
  
  //if the frame is well encoded
  
  if (got_pkt) {
  
      pkt.stream_index = this->st->index;
  
      pkt.pts = av_rescale_q_rnd(pkt.pts, this->pCodecCtx->time_base, this->st->time_base, AVRounding(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
  
      if (av_write_frame(this->outFormatCtx, &pkt) < 0)
  
          throw myExceptions("Error: failed to write video frame. FfmpegEncoder.cpp l:68\n");
  
  }
  
  }
  
  
  
  void FfmpegEncoder::FillYuvImage(AVFrame * pict, int frame_index, int width, int height)
  
  {
  
  int x, y, i;
  
  
  
  i = frame_index;
  
  
  
  for (y = 0; y < height; y++)
  
  {
  
      for (x = 0; x < width / 2; x++)
  
          pict->data[0][y * pict->linesize[0] + x] = x + y + i * 3;
  
  }
  
  for (y = 0; y < height; y++)
  
  {
  
      for (x = 0; x < width / 2; x++)
  
      {
  
          pict->data[1][y * pict->linesize[1] + x] = 128 + y + i * 2;
  
          pict->data[2][y * pict->linesize[2] + x] = 64 + y + i * 5; //segault here
  
      }
  
  }
  
  }

  The "FillYuvImage" method is copied from a FFMPEG example, but It does not work for me. If I don’t call it, the "av_write_frame" function won’t work (segfault too).

  EDIT : Here is my output context and codec initialization.

  FfmpegEncoder::FfmpegEncoder(char *url)
  
  {
  
  AVRational      tmp_time_base;
  
  AVDictionary*   options = NULL;
  
  
  
  this->pCodec = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  if (this->pCodec == NULL)
  
      throw myExceptions("Error: Can't initialize the encoder. FfmpegEncoder.cpp l:9\n");
  
  
  
  this->pCodecCtx = avcodec_alloc_context3(this->pCodec);
  
  
  
  //Alloc output context
  
  if (avformat_alloc_output_context2(&outFormatCtx, NULL, "rtsp", url) < 0)
  
      throw myExceptions("Error: Can't alloc stream output. FfmpegEncoder.cpp l:17\n");
  
  
  
  this->st = avformat_new_stream(this->outFormatCtx, this->pCodec);
  
  
  
  if (this->st == NULL)
  
      throw myExceptions("Error: Can't create stream . FfmpegEncoder.cpp l:22\n");
  
  
  
  av_dict_set(&options, "vprofile", "main", 0);
  
  av_dict_set(&options, "tune", "zerolatency", 0);
  
  
  
  tmp_time_base.num = 1;
  
  tmp_time_base.den = 60;
  
  
  
  //TODO : parse these values
  
  this->pCodecCtx->bit_rate = 3000000;
  
  this->pCodecCtx->width = 1280;
  
  this->pCodecCtx->height = 720;
  
  //This set the fps. 60fps at this point.
  
  this->pCodecCtx->time_base = tmp_time_base;
  
  //Add a intra frame every 12 frames
  
  this->pCodecCtx->gop_size = 12;
  
  this->pCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
  //Open Codec, using the context + x264 options
  
  if (avcodec_open2(this->pCodecCtx, this->pCodec, &options) < 0)
  
      throw myExceptions("Error: Can't open the codec. FfmpegEncoder.cpp l:43\n");
  
  
  
  if (avcodec_copy_context(this->st->codec, this->pCodecCtx) != 0) {
  
      throw myExceptions("Error : Can't copy codec context. FfmpegEncoder.cpp : l.46");
  
  }
  
  
  
  av_dump_format(this->outFormatCtx, 0, url, 1);
  
  
  
  if (avformat_write_header(this->outFormatCtx, NULL) != 0)
  
      throw myExceptions("Error: failed to connect to RTSP server. FfmpegEncoder.cpp l:48\n");
  
  }

• Cleaning up after av_frame_get_buffer

  4 novembre 2016, par Jason C

  There are two aspects of my question. I’m using libav, ffmpeg, 3.1.

  ---

  First, how do you appropriately dispose of a frame whose buffer has been allocated with av_frame_get_buffer ? E.g. :

  AVFrame *frame = av_frame_alloc();
  
  frame->width = ...;
  
  frame->height = ...;
  
  frame->format = ...;
  
  av_frame_get_buffer(frame, ...);

  Do any buffers have to be freed manually, beyond the call to av_frame_free(frame) ? The documentation doesn’t mention anything special, but in my experience the ffmpeg documentation often leaves out important details, or at least hides them in places far away from the obvious spots. I took a look at the code for av_frame_free and av_frame_unref but it branched out quite a bit and I couldn’t quite determine if it covered everything.

  ---

  Second, if something beyond av_frame_free needs to be done, then is there any catch-all way to clean up a frame if you don’t know how its data has been allocated ? For example, assuming someBuffer is already allocated with the appropriate size :

  AVFrame *frame2 = av_frame_alloc();
  
  frame2->width = ...;
  
  frame2->height = ...;
  
  frame2->format = ...;
  
  av_image_fill_arrays(frame2->data, frame2->linesize, someBuffer, 
  
                       frame2->format, frame2->width, frame2->height, 1);

  Is there a way to free both frame and frame2 in the above examples using the exact same code ? That is frame and its data should be freed, and frame2 should be freed, but not someBuffer, since libav did not allocate it.

• ffmpeg sws_scale converting from YUV420P to RGB24 results in wrong color values

  3 novembre 2016, par Drazurh

  I’m using sws_scale to convert a video from YUV420P to RGB24. The resulting RGB values are wrong, looking much more saturated/contrasted. For example, the first pixel should have an RGB value of (223,73,30) but using sws_scale results in (153,0,0).

  Here’s the code I’m using :

  uint8_t *buffer = NULL;
  
  int numBytes;
  
  // Determine required buffer size and allocate buffer
  
  numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
  
                             pCodecCtx->height);
  
  buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
  // Assign appropriate parts of buffer to image planes in pFrameRGB
  
  // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
  
  // of AVPicture
  
  std::cout << "Filling picture of size " << pCodecCtx->width <<" x "<height << std::endl;
  
  avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
  
                  pCodecCtx->width, pCodecCtx->height);
  
  
  
  
  
  
  
  // initialize SWS context for software scaling
  
  std::cout << "initializing SWS context\n";
  
  sws_ctx = sws_getContext(pCodecCtx->width,
  
      pCodecCtx->height,
  
      pCodecCtx->pix_fmt,
  
      pCodecCtx->width,
  
      pCodecCtx->height,
  
      PIX_FMT_RGB24,
  
      SWS_FAST_BILINEAR,
  
      NULL,
  
      NULL,
  
      NULL
  
  );
  
  
  
  while(frameFinished == 0)
  
  {
  
      if(av_read_frame(pFormatCtx, &packet)<0){
  
          std::cerr << "Could not read frame!\n";
  
          return false;
  
      }
  
  
  
      if(packet.stream_index==videoStream)
  
      {
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
      }
  
  
  
  }
  
  
  
  sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
  
            pFrame->linesize, 0, pCodecCtx->height,
  
            pFrameRGB->data, pFrameRGB->linesize);

  The values in pFrameRGB are incorrect. I’ve tried troubleshooting this for hours :-( Any ideas on how to track down my mistake ?

  Here’s a link to the repo. The offending code is in Icosahedron Video Player/mesh.cpp, Mesh::LoadVideo and Mesh::NextFrame().