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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.

• ffmpeg x11grab moov atom not found

  30 mars 2021, par Jintor

  2 FFMPEG process

  


  (1) generating a ffmpeg x11grab to a .mp4
(2) take the .mp4 and restream it simultaneously to multiple rtmp endpoints

  


  ISSUE the generated file in (1) have this error "moov atom not found"

  


  This is the command that generate (1) :

  


  ffmpeg -re -y -f x11grab -draw_mouse 0 -framerate 30 
-video_size $RESOLUTION -i :$DISPLAY_NUM -c:a aac -c:v libx264 
-movflags +faststart -preset ultrafast -crf 28 -refs 4 -qmin 4 
-pix_fmt yuv420p -filter:v fps=30 file.mp4


  


  in the (2) => when I try to ffmpeg -i file.mp4 output somewhere : I get "moov atom not found" so the (2) can't read or open (1).

  


  What I'm I missing

  


  in (1) -movflags +faststart doesn't seem to fix the issue

  


  ••••••• EDIT : more details on the context ••••••

  


  I'm using openvidu : webrtc with kurento and coturn.

  


  The record feature creates a .mp4 on the fly as the chat is going on.

  


  To start the recording, there is an API call i can make to my server and it automatically stops when all users leaves the chatroom OR do an other api call to stop. see composed video in this link https://docs.openvidu.io/en/2.17.0/advanced-features/recording/

  


  openvidu have also webhooks.

  


  My problem is not how to stop ffmpeg, but getting FFMPEG to encode while the mp4 or other is being generated "on the fly".

  


  There is 2 options :

  


  OPTION 1 : individual => 1 .webm per camare => this .webm ffmpeg can restream as hls or RTMP => it's working.

  


  OPTION 2 : ** but the issue is with "Composed" video => it's using ffmpeg to x11grab the session... but it's mp4 without moov ato, so ffmpeg don't do anything with this.

  


  see the composed.sh script here
https://github.com/OpenVidu/openvidu/blob/master/openvidu-server/docker/openvidu-recording/scripts/composed.sh

  


• FFMpeg outputs empty stream/file in C#

  15 juin 2017, par Dark0Matter

  I’m making a bot for discord, and I’m currently trying to use ffmpeg to stream an audio file through voice chat. (Which, many other people succeeded in doing it)

  So basically, I’m using libsodium.dll + opus.dll + ffmpeg.exe to turn an mp3 file into a stream using ffmpeg, and output it.

  This is my "CreateStream" function which starts ffmpeg and turns the mp3 file into a stream/pipe.

      private Process CreateStream(string path)
  
      {
  
          var ffmpeg = new ProcessStartInfo
  
          {
  
              FileName = "ffmpeg.exe",
  
              //Arguments = $"-hide_banner -loglevel panic -i \"{path}\" -ac 2 -f s16le -ar 48000 pipe:1",
  
              Arguments = $"-i {path} -ac 2 -f s16le -ar 48000 pipe:1",
  
              //Arguments = $"-i {path} -ac 2 -f s16le -ar 48000 testingtesting.mp3",
  
              UseShellExecute = false,
  
              RedirectStandardOutput = true,
  
          };
  
          return Process.Start(ffmpeg);
  
      }

  The commented arguments are the other arguments that I’ve tried. (e.g. the last commented arguments line was an attempt to output it to a file instead of a stream, and the file turned out to be empty)

  So basically, my current arguments are

  Arguments = $"-i {path} -ac 2 -f s16le -ar 48000 pipe:1"

  (where pipe:1 is replaceable by any filename such as test.wav)

  and here’s my problem in case you didn’t catch it :

  ffmpeg always outputs empty streams/files.

  Here’s the output that I got in the console.
  https://pastebin.com/zvGgsZZ6

  So my question is,

  Am I using the wrong arguments ?

  And if so, what other arguments can I try to get it fixed ?

  Tl ;dr : ffmpeg outputs empty data to a stream, and it does the same thing when the pipe is replaced by a .wav/.mp3 file.

  EDIT1 : After some time of waiting, I got this : https://pastebin.com/y8rjnsMb

  EDIT2 : I searched for more argument combinations that worked for other people and stumbled upon Arguments = $"-i \"path\" -ab 48000 -f mp3 test.mp3",
  when I tried writing to test.mp3, it worked, but the quality was low.
  Then I tried replacing test.mp3 with pipe:1, but that didn’t work. Help ?