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• FFmpeg avcodec_encode_video2 access violation

  28 février 2016, par JustPingo

  I’ve been trying to encode a frame using FFmpeg with Visual C++. Here is how I do it.
  I first have a planar RGB24 image buffer. I convert it to planar YUV using the following rule :

  Y = ((66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
  
  U = ((-38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
  
  V = ((112 * R - 94 * G - 18 * B + 128) >> 8) + 128;

  I implemented it like this :

  void rgb8toYuv(uchar* rgb, uchar* yuv, uint pixelAmount) {
  
      uchar r, g, b;
  
      for (uint i = 0; i < pixelAmount; i++) {
  
          r = rgb[3 * i];
  
          g = rgb[3 * i + 1];
  
          b = rgb[3 * i + 2];
  
          yuv[3 * i] = ((66 * r + 129 * g + 25 * b + 128) >> 8) + 16;
  
          yuv[3 * i + 1] = ((-38 * r - 74 * g + 112 * b + 128) >> 8) + 128;
  
          yuv[3 * i + 2] = ((112 * r - 94 * g - 18 * b + 128) >> 8) + 128;
  
      }
  
  }

  I open everything like this (I’m using malloc because I’m used to it in C and it’s my first C++ program, I guess it shouldn’t cause any problem ?) :

  AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  AVFormatContext* outContext;
  
  avformat_alloc_output_context2(&outContext, NULL, "mp4", filepath);
  
  
  
  AVStream* video = avformat_new_stream(outContext, codec);
  
  video->codec->bit_rate = VIDEOBITRATE;
  
  video->codec->width = VIDEOWIDTH;
  
  video->codec->height = VIDEOHEIGHT;
  
  video->time_base = fps;
  
  video->codec->gop_size = 10;
  
  video->codec->max_b_frames = 1;
  
  video->codec->pix_fmt = AV_PIX_FMT_YUV420P;
  
  video->codec->codec_id = AV_CODEC_ID_H264;
  
  video->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  
  
  
  avio_open(&outContext->pb, filepath, AVIO_FLAG_READ_WRITE);
  
  avformat_write_header(outContext, NULL);
  
  
  
  AVFrame* frame = av_frame_alloc();
  
  frame->width = VIDEOWIDTH;
  
  frame->height = VIDEOHEIGHT;
  
  frame->format = AV_PIX_FMT_YUV420P;

  Then, here is the function I use to encode a frame :

  void encodeFrame(uint currentFrame, uchar* data) { // RGB data
  
      uchar* yuvData = (uchar*) malloc(videoWidth * videoHeight * 3);
  
      rgb8toYuv(data, yuvData, videoWidth * videoHeight);
  
      av_image_fill_arrays(frame->data, frame->linesize, yuvData, AV_PIX_FMT_YUV420P, videoWidth, videoHeight, 3); // I'm not sure about that 3, I couldn't find any documentation about it
  
  
  
      AVPacket* packet = (AVPacket*) malloc(sizeof(AVPacket));
  
      memset(packet, 0, sizeof(AVPacket));
  
      av_init_packet(packet);
  
      packet->data = NULL;
  
      packet->size = 0;
  
  
  
      frame->pts = currentFrame; // I don't know if this is corrrect too
  
      avcodec_encode_video2(video->codec, packet, frame, NULL);
  
      av_interleaved_write_frame(outContext, packet);
  
      av_packet_unref(packet);
  
  
  
      free(yuvData);
  
      free(packet);
  
  }

  However, this causes an Access violation writing location 0x00000000 on avcodec_encode_video2. I checked the errors returned by every of FFmpeg’s functions, and it seems like they all work except av_image_fill_arrays that returns a weird 1382400 error, although according to the debugger’s RAM-viewing tool, everything gets filled correctly.

  It seems like avcodec_encode_video2 tries to access a NULL object that shouldn’t be, however I can’t find what it could be, as I followed a lot of sources example, and I don’t know what I did wrong.

  Thanks in advance !

  EDIT : After applying the fix suggested by Edgar Rokyan (which is setting the 4th argument to an int pointer), I now get an access violation on 0x00000024, still with avformat_alloc_output_context2. I believe the problem is similar, but I still can’t find anything.

• FFMPEG / libav : How is UYVY422 written inside AVFrame structure ?

  26 avril 2016, par Sir DrinksCoffeeALot

  I’m trying to copy frame data from AVFrame structure to a buffer. I know how to do that with YUV420P format since Y data is stored inside AVFrame frame->data[0], U data is stored inside AVFrame frame->data[1] and V data is stored inside AVFrame frame->data[2], so it was easy to memcpy() Y,U and V data separately + it’s planar format so i was able to do that with ease :

  for (y = 0; y < height; y++)
  
      {
  
          memcpy(buffer + y*frame->linesize[0], frame->data[0] + y*frame->linesize[0], width);
  
      }
  
  
  
      buffer += ySize;
  
  
  
      for (y = 0; y < height / 2; y++)
  
      {
  
          memcpy(buffer + y*frame->linesize[1], frame->data[1] + y*frame->linesize[1], width / 2);
  
      }
  
  
  
      buffer += uSize;
  
  
  
      for (y = 0; y < height / 2; y++)
  
      {
  
          memcpy(buffer + y*frame->linesize[2], frame->data[2] + y*frame->linesize[2], width / 2);
  
      }

  But when it comes to UYVY422 i have no idea how the data is stored inside the structure. I have general knowledge about UYVY422 format and that it’s written like it name suggests UYVYUYVYUYVY... and so on. But my question is how do i know how much data is stored in AVFrame frame->data[0], AVFrame frame->data[1] and AVFrame frame->data[2] field so i can memcpy() exact amount to the buffer ?

• avcodec/v4l2_buffers : Add handling for NV21 and YUV420P

  22 mars 2018, par Dave Stevenson

  avcodec/v4l2_buffers : Add handling for NV21 and YUV420P
  The single planar support was for NV12 only.
  
  Add NV21 and YUV420P support.
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  

  • [DH] libavcodec/v4l2_buffers.c