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• ffmpeg 1080p50 50fps unsupported on some samsung models, resulting in Error

  15 octobre 2019, par Sambir

  So I use FFMPEG for live transcoding using nvenc gpu acceleration. I recently did some minor improvements by upping the framerate to 1080p50 instead of 1080p25.

  I noticed that this caused "error" messages on some samsung models. I was wondering if it is due to my code, can we up the compatibility or are the tv’s just unable to playback 1080p50 which I think is really strange.

  This is the command I use :

  ffmpeg -hwaccel cuvid -vcodec h264_cuvid -vcodec h264_cuvid -i 'rtmp://127.0.0.1:8001/input/bla' -max_muxing_queue_size 1024 -map 0:v -map 0:a -vf yadif_cuda=1 -acodec libfdk_aac -b:a 128k -c:v h264_nvenc -preset llhq -vprofile high -level 4.2 -rc:v vbr -qmin:v 18 -qmax:v 42 -b:v 6M -maxrate 6M -bufsize 12M -threads 0 -r 50 -g 200 -f flv 'rtmp://127.0.0.1:8001/input/test'

  Like 80% of the models, samsung/lg/sony are able to play it but some small amount of samsung tv’s give stream error. I have a feeling it is just the high framerate where the tv/app is unable to play it back resulting in "streaming error". Because on even older lg models the stream plays back just perfectly. It does not seem to be a format or something...

• Extract different camera frames (multiplex)

  22 août 2016, par Mike Issa

  I have a sequential multiplexed video with 3 cameras. These videos are being converted from VHS to DVD (.VOB format). I am using ffmpeg to extract all frames in .JPG format.

  I want to write a python script that scans for a certain object in the frame (like a constant/static object in the background) and organizes all the frames containing that object into a folder. This is the only way I can think of to separate the camera views, because as the video progresses, one of the cameras turns off for a few minutes and then turns back on, ruining the interval of 3-frames-per-camera-view sequence*.

  • I tried writing a python script that extracts every third frame (starting from the first frame for camera 1, second frame for camera 2, third frame for camera 3) into separate folders, but this did not bode well when I found out that one of the cameras switches off and then back on.

  I tried a "detection patch" method using VirtualDub found in this forum, but it didn’t work for me (not sure why).

  Should I be using numpy or openCV to find a certain block of pixels in each frame to do the organizing of camera views, or is there a simpler way ?

• Windows Pipes STDIN and STDOUT Parent Child proc communication IPC FFMPEG

  15 octobre 2018, par Evren Bingøl

  I am writing a simple WINDOWS app which demonstrates piping,

  I pass byte size data down to child proc, increment the value and send the char size data back to parent and loop until it reaches MAX_CHAR
  Pretty much demonstration of "i++" with IPC.

  Parent Process

  while(i<256){
  
      bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, sizeof(char), &dwWritten, NULL);
  
      bSuccess = ReadFile(g_hChildStd_OUT_Rd, chBuf, sizeof(char), &dwRead, NULL); // IF THERE IS NO FFLUSH IT BLOCKS
  
  }

  And in Child

  while (i<256){
  
          byte data=0;
  
          fread(&data, sizeof(char), 1, stdout);
  
          data++;
  
          fwrite(&data, sizeof(char), 1, stdout);
  
          //fflush(stdout); IF I DO NOT HAVE THIS  PARENT BLOCKS ON READ
  
  }

  First of all if I do not FFLUSH child proc stdout, the parent blocks on reading child’s stdout.

  How can one run this code without having to fflush child’s stdout.

  Closing the pipe after child’s first write is not an option as it is in a loop and needs to execute 256 times.

  more generically I want the child to write N bytes to parent, parent read that N bytes do something and write back to child another N bytes and child does something with that N bytes and write to parent N bytes. This happens M times.

  thing is I can not use fflush because my final goal is to use a child process that is not implemented by me.

  My final goal is to pipe data to FFMPEG encode the data and read back from the stdin and do this over and over again with out having to fork a new FFMPEG process for each image frame but rather fork one instance of FFMPEG and pipe data in and read data out from it. And since I did not implement ffmpeg and I can not change the source code.

  thanks

  Thanks