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• yet another screenshot encoding exercise with ffmpeg - stuck at getting AVFrame from ALT::CImage - VC++

  11 septembre 2013, par sith

  Total AV newbee here - trying to learn the ropes on using FFMpeg functions to encode movies. On searching for tutorials I found a few similar questions that I have linked here for reference :

  Encoding a screenshot into a video using FFMPEG

  [Libav-user] Encoding a screenshot into a video using FFMPEG

  Save bitmap to video (libavcodec ffmpeg)

  When converting from RGB to YUV using ffmpeg the video file the color is spread why ?

  How to convert RGB from YUV420p for ffmpeg encoder ?

  Encode bmp sequence with libavcodec...Help !

  Not able to encode image with ffmpeg

  For my setup FFMPEG is on VS12 - VC++ with MFC on win7.

  With the help of above samples, I am able to get "some" output from the encoder, but I am not sure in what format or state the output has been encoded. Neither VLC nor WMP can play this file. It does not even seem to recognize the metadata in the file to display the FPS or video length. What would normally cause that ? Also any pointers on what could be going wrong and how to approach fixing the problems would be great. [1]

  Here is the flow of my code :

  Step1 : capture desktop on to a CImg :

  int W=GetSystemMetrics(SM_CXSCREEN), H=GetSystemMetrics(SM_CYSCREEN), bpp=24; 
  
  CImage cImg; cImg.Create(W,H,bpp) 
  
  HDC hDC = cImg.GetDC(); 
  
  CWindowDC winDC(GetDesktopWindow()); 
  
  
  
  BitBlt(hDC, 0,0, rez.W(), rez.H(), winDC.m_hDC, 0, 0, SRCCOPY);

  At this point I am able to dump a screen shot into a bmp file -
  using cImg.Save( _T("test.bmp"), Gdiplus::ImageFormatBMP) ;

  Step2 : Extract the BMP bits from the CImg.

  HBITMAP hBitmap = (HBITMAP)cImg;
  
  HDC memDC = CreateCompatibleDC(NULL);
  
  SelectObject( memDC, hBitmap );
  
  
  
  BITMAPINFO bmi; // initialized bmi with {W,-H, plane=1, bitCount=24, comp=BI_RGB, size=W*H*3 }
  
  << removed bmi init code for conciseness. >>>
  
  
  
  BYTE *rgb24Data = new BYTE[W*H*3]; // 3 for 24bpp. 4 for 32...
  
  int ret = GetDIBits(memDC, hBitmap, 0, H, rgb24Data, &bmi, DIB_RGB_COLORS);

  At this point I faithfully believe rgb24Data points to pixel data :) - copied out of the cImg bitmap

  Step 3 : next I try to create an AV frame with the rgb24Data got from this CImg. Also this is where I have a massive knowledge gap. I am going to try and recover

  // setup the codecs and contexts here as per mohM's post
  
  
  
  AVCodec *currCodec = avcodec_find_encoder(CODEC_ID_MPEG4);
  
  
  
  AVCodecContext *codeCtxt = avcodec_alloc_context();  // init this with bate=400k, W, H,
  
  << removed codeCtxt init code for conciseness. >>>   //  time base 1/25, gop=10, max_b=1, fmt=YUV420
  
  
  
  avcodec_open(codeCtxt, currCodec);
  
  
  
  SwsContext *currSWSCtxt = sws_getContext( W, H, AV_PIX_FMT_RGB24, // FROM
  
                                            W, H, AV_PIX_FMT_YUV420P, // TO
  
                                            SWS_FAST_BILINEAR,
  
                                            NULL, NULL, NULL);
  
  
  
  // allocate and fill AVFrame
  
  int numBytes = avpicture_get_size(PIX_FMT_YUV420P, W, H);
  
  uint8_t *buffer=new uint8_t[numBytes];
  
  AVFrame *avFrame = avcodec_alloc_frame();
  
  avpicture_fill( (AVPicture*)avFrame, buffer, PIX_FMT_YUV420P, W, H );

  Step 4 : transform the data frame into YUV420P as we fill the frame.

  uint8_t * inData[1] = { rgb24Data };
  
  int inLinesize[1] = { 3*W }; // RGB stride
  
  sws_scale( currSWSCtxt, inData, inLinesize, 0, H,
  
             avFrame->data, avFrame->linesize);

  step 5 encode the frame and write out the output buffer into a file.

  int out_size = avcodec_encode_video( codeCtxt,
  
                                       outBuf,
  
                                       outBufSize,
  
                                       avFrame );
  
  
  
  fwrite(outBuf, 1, outBufSize, outFile );

  finally I close the file off with [0x00 0x00 0x01 0xb7]

  The first hint of things gone haywire is that for a 50 screens of 1920X1080 at 24bpp encoded at 25fps gives me a 507MB unplayable-mpeg file.

  As mentioned earlier, neither VLC nor WMP can play this file nor they even recognize the metadata in the file to display the FPS or video length. What would normally cause that ? Also any pointers on what could be going wrong and how to approach fixing the problems would be great. [2]

  Any guidance is much appreciated.

• how can I get the length of an video in order to validate django form before upload can begin ?

  10 juillet 2013, par GetItDone

  I have an app running on heroku that allows users to upload videos, then I use ffmpeg to preform 3 tasks using celery and redis-to-go :

  1) Check the format and if it isn't already mp4, convert it to mp4.
  
  2) Extract a 3 minute clip, in mp4 format
  
  3) Grab an image from the video

  The problem is that I want to verify the video length before the video is uploaded and the three tasks are run since I want to make sure all videos are at least 15 minutes, and if not I want to raise a ValidationError. So when validating the form, I want to do something like this :

  def clean(self, *args, **kwargs):        
  
      data = super(ContentTypeRestrictedVideoField, self).clean(*args, **kwargs)
  
  
  
      file = data.file
  
      try:
  
          content_type = file.content_type
  
          main, extension = content_type.split('/')
  
          if content_type in self.content_types:
  
              if file._size > self.max_upload_size:
  
                  raise forms.ValidationError(_('Please keep filesize under %s. Current filesize %s') % (filesizeformat(self.max_upload_size), filesizeformat(file._size)))
  
              if VIDEO_LENGTH < MINIMUM_LENGTH:
  
                  raise forms.ValidationError(_('Please make sure video file is at least %s. Current video length %s') % (MINIMUM_LENGTH, VIDEO_LENGTH)
  
          else:
  
              raise forms.ValidationError(_('File type is not supported. File must be mov, flv, avi, mpeg, wmv, or mp4.'))
  
      except AttributeError:
  
          pass        
  
  
  
      return data

  What could I do for VIDEO_LENGTH and MINIMUM_LENGTH ? I read that ffprobe could be used for getting the duration, but it isn't available with the buildpack I am using and I am very inexperienced. I can't just validate file size because it can vary greatly depending on numerous factors. Anyone have any solution as to what I could try ? Thanks

• How to use FFMPEG commands

  26 septembre 2013, par Shashank Agarwal

  In android i am making an app in which it will record an video and crop the video from center for doing so i found FFMPEG over google. I followed http://dmitrydzz-hobby.blogspot.in/2012/04/how-to-build-ffmpeg-and-use-it-in.html

  It works fine but i want to know how to use this `ffmpeg -y -i /sdcard/videokit/short.mp4 -vf crop=100:100:0:0 -s 320x240 -r 15 -aspect 3:4 -ab 12288 -vcodec mpeg4 -b 2097152 -sample_fmt s16 /sdcard/videokit/out.mp4

  ` video cropping command and Where to write this command.

  I have tried this (for concatenation just to check about how to use ffmpeg command )

  public class MainActivity extends Activity {
  
  private static native int logFileInfo(String[] args);
  
  String pathOut = "/storage/sdcard/12.mp3";
  
  String pathInM = "/storage/sdcard/23.mp3";
  
  String pathIn = "/storage/sdcard/out.mp3";
  
  @Override
  
  public void onCreate(Bundle savedInstanceState) {
  
      super.onCreate(savedInstanceState);
  
      setContentView(R.layout.activity_main);
  
      String[] args = {"ffmpeg",  "-i", "concat:", pathOut, "|",pathInM ,pathIn};
  
      logFileInfo(args);
  
      //logFileInfo("/storage/sdcard/12.mp3");
  
  }
  
  
  
  static
  
  {
  
      System.loadLibrary("mylib");
  
  }

  But i dont know what to write in mylib.c to execute this.somebody Please help