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• Blackmagic SDK - OpenGL Letterbox and FFMPEG

  18 mars 2015, par Marco Reisacher

  so I left my Idea using the DirectShow filters due to lack of Support of my needed Video formats.
  The native API uses OpenGL which i am a total beginner to.
  I stumbled upon the following problems :

  1. How to automatically apply a letterbox or pillarbox depending on the width and height of the Frame that gets passed to OpenGL (I’m using bpctrlanchormap.h to autosize everything and i get squeezed/stretched images)

  2. How to record a Video of the OpenGL stream (I looked around and saw that ffmpeg should be able to do so, but I can’t get it running.) Also what would be nice is Audio recording into the same file of a microphone

  I’m using the Blackmagic "Capture Preview" sample.

  This is the sourcecode that initialises the OpenGL renderer and passes the Frames

  #include "stdafx.h"
  
  #include <gl></gl>gl.h>
  
  #include "PreviewWindow.h"
  
  
  
  PreviewWindow::PreviewWindow()
  
  : m_deckLinkScreenPreviewHelper(NULL), m_refCount(1), m_previewBox(NULL), m_previewBoxDC(NULL), m_openGLctx(NULL)
  
  {}
  
  
  
  PreviewWindow::~PreviewWindow()
  
  {
  
      if (m_deckLinkScreenPreviewHelper != NULL)
  
      {
  
          m_deckLinkScreenPreviewHelper->Release();
  
          m_deckLinkScreenPreviewHelper = NULL;
  
      }
  
  
  
      if (m_openGLctx != NULL)
  
      {
  
          wglDeleteContext(m_openGLctx);
  
          m_openGLctx = NULL;
  
      }
  
  
  
      if (m_previewBoxDC != NULL)
  
      {
  
          m_previewBox->ReleaseDC(m_previewBoxDC);
  
          m_previewBoxDC = NULL;
  
      }
  
  }
  
  
  
  bool        PreviewWindow::init(CStatic *previewBox)
  
  {
  
      m_previewBox = previewBox;
  
  
  
      // Create the DeckLink screen preview helper
  
      if (CoCreateInstance(CLSID_CDeckLinkGLScreenPreviewHelper, NULL, CLSCTX_ALL, IID_IDeckLinkGLScreenPreviewHelper (void**)&amp;m_deckLinkScreenPreviewHelper) != S_OK)
  
      return false;
  
  
  
      // Initialise OpenGL
  
      return initOpenGL();
  
  }
  
  
  
  bool        PreviewWindow::initOpenGL()
  
  {
  
      PIXELFORMATDESCRIPTOR   pixelFormatDesc;
  
      int                     pixelFormat;
  
      bool                    result = false;
  
  
  
      //
  
      // Here, we create an OpenGL context attached to the screen preview box
  
      // so we can use it later on when we need to draw preview frames.
  
  
  
      // Get the preview box drawing context
  
      m_previewBoxDC = m_previewBox->GetDC();
  
      if (m_previewBoxDC == NULL)
  
          return false;
  
  
  
      // Ensure the preview box DC uses ARGB pixel format
  
      ZeroMemory(&amp;pixelFormatDesc, sizeof(pixelFormatDesc));
  
      pixelFormatDesc.nSize = sizeof(pixelFormatDesc);
  
      pixelFormatDesc.nVersion = 1;
  
      pixelFormatDesc.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL;
  
      pixelFormatDesc.iPixelType = PFD_TYPE_RGBA;
  
      pixelFormatDesc.cColorBits = 32;
  
      pixelFormatDesc.cDepthBits = 16;
  
      pixelFormatDesc.cAlphaBits = 8;
  
      pixelFormatDesc.iLayerType = PFD_MAIN_PLANE;
  
      pixelFormat = ChoosePixelFormat(m_previewBoxDC->m_hDC, &amp;pixelFormatDesc);
  
      if (SetPixelFormat(m_previewBoxDC->m_hDC, pixelFormat, &amp;pixelFormatDesc) == false)
  
          return false;
  
  
  
      // Create OpenGL rendering context
  
      m_openGLctx = wglCreateContext(m_previewBoxDC->m_hDC);
  
      if (m_openGLctx == NULL)
  
          return false;
  
      // Make the new OpenGL context the current rendering context so
  
      // we can initialise the DeckLink preview helper
  
      if (wglMakeCurrent(m_previewBoxDC->m_hDC, m_openGLctx) == FALSE)
  
          return false;
  
  
  
      if (m_deckLinkScreenPreviewHelper->InitializeGL() == S_OK)
  
          result = true;
  
  
  
      // Reset the OpenGL rendering context
  
      wglMakeCurrent(NULL, NULL);
  
  
  
      return result;
  
  }
  
  
  
  HRESULT         PreviewWindow::DrawFrame(IDeckLinkVideoFrame* theFrame)
  
  {
  
      // Make sure we are initialised
  
      if ((m_deckLinkScreenPreviewHelper == NULL) || (m_previewBoxDC == NULL) || (m_openGLctx == NULL))
  
          return E_FAIL;
  
  
  
      // First, pass the frame to the DeckLink screen preview helper
  
      m_deckLinkScreenPreviewHelper->SetFrame(theFrame);
  
  
  
      // Then set the OpenGL rendering context to the one we created before
  
      wglMakeCurrent(m_previewBoxDC->m_hDC, m_openGLctx);
  
  
  
      // and let the helper take care of the drawing
  
      m_deckLinkScreenPreviewHelper->PaintGL();
  
  
  
      // Last, reset the OpenGL rendering context
  
      wglMakeCurrent(NULL, NULL);
  
  
  
      return S_OK;
  
  }

• "Non-monotonous DTS in output stream 0:0 This may result in incorrect timestamps in the output file." error

  1er août 2019, par petaire

  I’m trying to go from .mkv to .mp4 through ffmpeg. Normally I would use

  ffmpeg -i $1 -codec copy -strict -2 $2

  But on this particular file, I get this error, like, A LOT :

  Non-monotonous DTS in output stream 0:0; previous: 49189232, current: 49189232; changing to 49189233. This may result in incorrect timestamps in the output file.

  I guess it has something to do with the DTS :

  [mp4 @ 0x7f8b14001200] Invalid DTS: 14832 PTS: 13552 in output stream 0:0, replacing by guess
  
  [mp4 @ 0x7f8b14001200] Invalid DTS: 15472 PTS: 12272 in output stream 0:0, replacing by guess

  I would not care if the result was ok, but the sound is out of sync, and the video is "stuttering". Feels like everything is out of sync.

  I’ve tried a lot of things, including -async 1 -vsync 1 , but nothing seems to work.

  Here’s some mediainfo :

  Complete name                            : /Users/petaire/Desktop/CNEWS-2019-07-23_16-00-00h.mkv
  
  Format                                   : Matroska
  
  Format version                           : Version 2
  
  File size                                : 1.19 GiB
  
  Movie name                               : Time-2019-07-23_16:00
  
  Writing application                      : Tvheadend 4.3-1801~g7f952c2ed
  
  Writing library                          : Tvheadend Matroska muxer
  
  Original source form                     : TV
  
  Comment                                  : Time recording
  
  IsTruncated                              : Yes
  
  DATE_BROADCASTED                         : 2019-07-23 16:00:00
  
  
  
  Video
  
  ID                                       : 1
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : High@L4
  
  Format settings                          : CABAC / 4 Ref Frames
  
  Format settings, CABAC                   : Yes
  
  Format settings, ReFrames                : 4 frames
  
  Codec ID                                 : V_MPEG4/ISO/AVC
  
  Width                                    : 1 920 pixels
  
  Height                                   : 1 080 pixels
  
  Display aspect ratio                     : 16:9
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 25.000 fps
  
  Standard                                 : Component
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 8 bits
  
  Scan type                                : MBAFF
  
  Scan type, store method                  : Interleaved fields
  
  Scan order                               : Top Field First
  
  Language                                 : English
  
  Default                                  : Yes
  
  Forced                                   : No
  
  Color range                              : Limited
  
  Color primaries                          : BT.709
  
  Transfer characteristics                 : BT.709
  
  Matrix coefficients                      : BT.709
  
  
  
  Audio
  
  ID                                       : 2
  
  Format                                   : E-AC-3
  
  Format/Info                              : Enhanced AC-3
  
  Commercial name                          : Dolby Digital Plus
  
  Codec ID                                 : A_EAC3
  
  Bit rate mode                            : Constant
  
  Bit rate                                 : 128 Kbps
  
  Channel(s)                               : 2 channels
  
  Channel layout                           : L R
  
  Sampling rate                            : 48.0 KHz
  
  Frame rate                               : 31.250 fps (1536 SPF)
  
  Compression mode                         : Lossy
  
  Delay relative to video                  : -757ms
  
  Language                                 : French
  
  Service kind                             : Complete Main
  
  Default                                  : Yes
  
  Forced                                   : No
  
  
  
  Text
  
  ID                                       : 3
  
  Format                                   : DVB Subtitle
  
  Codec ID                                 : S_DVBSUB
  
  Codec ID/Info                            : Picture based subtitle format used on DVBs
  
  Language                                 : French
  
  Default                                  : Yes
  
  Forced                                   : No

  Any idea ?

• How AVCodecContext bitrate, framerate and timebase is used when encoding single frame

  28 mars 2023, par Cyrus

  I am trying to learn FFmpeg from examples as there is a tight schedule. The task is to encode a raw YUV image into JPEG format of the given width and height. I have found examples from ffmpeg official website, which turns out to be quite straight-forward. However there are some fields in AVCodecContext that I thought only makes sense when encoding videos(e.g. bitrate, framerate, timebase, gopsize, max_b_frames etc).

  


  I understand on a high level what those values are when it comes to videos, but do I need to care about those when I just want a single image ? Currently for testing, I am just setting them as dummy values and it seems to work. But I want to make sure that I am not making terrible assumptions that will break in the long run.

  


  EDIT :

  


  Here is the code I got. Most of them are copy and paste from examples, with some changes to replace old APIs with newer ones.

  


  #include "thumbnail.h"
#include "libavcodec/avcodec.h"
#include "libavutil/imgutils.h"
#include 
#include 
#include 

void print_averror(int error_code) {
    char err_msg[100] = {0};
    av_strerror(error_code, err_msg, 100);
    printf("Reason: %s\n", err_msg);
}

ffmpeg_status_t save_yuv_as_jpeg(uint8_t* source_buffer, char* output_thumbnail_filename, int thumbnail_width, int thumbnail_height) {
    const AVCodec* mjpeg_codec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
    if (!mjpeg_codec) {
        printf("Codec for mjpeg cannot be found.\n");
        return FFMPEG_THUMBNAIL_CODEC_NOT_FOUND;
    }

    AVCodecContext* codec_ctx = avcodec_alloc_context3(mjpeg_codec);
    if (!codec_ctx) {
        printf("Codec context cannot be allocated for the given mjpeg codec.\n");
        return FFMPEG_THUMBNAIL_ALLOC_CONTEXT_FAILED;
    }

    AVPacket* pkt = av_packet_alloc();
    if (!pkt) {
        printf("Thumbnail packet cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_PACKET_FAILED;
    }

    AVFrame* frame = av_frame_alloc();
    if (!frame) {
        printf("Thumbnail frame cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_FRAME_FAILED;
    }

    // The part that I don't understand
    codec_ctx->bit_rate = 400000;
    codec_ctx->width = thumbnail_width;
    codec_ctx->height = thumbnail_height;
    codec_ctx->time_base = (AVRational){1, 25};
    codec_ctx->framerate = (AVRational){1, 25};

    codec_ctx->gop_size = 10;
    codec_ctx->max_b_frames = 1;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    int ret = av_image_fill_arrays(frame->data, frame->linesize, source_buffer, AV_PIX_FMT_YUV420P, thumbnail_width, thumbnail_height, 32);
    if (ret < 0) {
        print_averror(ret);
        printf("Pixel format: yuv420p, width: %d, height: %d\n", thumbnail_width, thumbnail_height);
        return FFMPEG_THUMBNAIL_FILL_FRAME_DATA_FAILED;
    }

    ret = avcodec_send_frame(codec_ctx, frame);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to send frame to encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    ret = avcodec_receive_packet(codec_ctx, pkt);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to receive packet from encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    // store the thumbnail in output
    int fd = open(output_thumbnail_filename, O_CREAT | O_RDWR);
    write(fd, pkt->data, pkt->size);
    close(fd);

    // freeing allocated structs
    avcodec_free_context(&codec_ctx);
    av_frame_free(&frame);
    av_packet_free(&pkt);
    return FFMPEG_SUCCESS;
}