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• Is there a way to filter out I/B/P frames in an MPEG Video stream and access the macroblock information ?

  5 janvier 2018, par Viktor Vix Jančík

  I am trying make a program for video analysis of MPEG streams in C or C++.

  I was able to find out the frame types in a video file using

  ffprobe -show_frames -pretty File.mpg | grep 'pict_type' > pict_type.txt

  However based on the order of the frames, it seems that they are in "display" (IBBPBBP...) order not in "transmission" order (IPBBPBBPBB...) and it’s not exactly ideal way of doing things as I can’t assure the command didn’t skip any frames or anything as it’s outside of my program.

  I have tried OpenCV, but it appears the information I require is too low-level for OpenCV and I believe the solution lies in ffmpeg or libavcodec but the documentation is a nightmare past the CLI. Although I am open to other solutions !

  The information I require are :

  • The type of each frame (I, B, or P)
  • The total number of macroblocks inside a frame
  • The number of intra-coded macroblocks inside a P frame
  • The number of both forward and backward predicted macroblocks inside a B frame
  • The number of just backward predicted macroblocks inside a B frame
  • The number of just forward predircted macroblocks inside a B frame

  I would be very grateful for your help !

• Is there a way to filter out I/B/P frames in an MPEG Video stream and access the macroblock information ?

  1er mars 2014, par Vixian

  I am trying make a program for video analysis of MPEG streams in C or C++.

  I was able to find out the frame types in a video file using

  ffprobe -show_frames -pretty File.mpg | grep 'pict_type' > pict_type.txt

  However based on the order of the frames, it seems that they are in "display" (IBBPBBP...) order not in "transmission" order (IPBBPBBPBB...) and it's not exactly ideal way of doing things as I can't assure the command didn't skip any frames or anything as it's outside of my program.

  I have tried OpenCV, but it appears the information I require is too low-level for OpenCV and I believe the solution lies in ffmpeg or libavcodec but the documentation is a nightmare past the CLI. Although I am open to other solutions !

  The information I require are :

  • The type of each frame (I, B, or P)
  • The total number of macroblocks inside a frame
  • The number of intra-coded macroblocks inside a P frame
  • The number of both forward and backward predicted macroblocks inside a B frame
  • The number of just backward predicted macroblocks inside a B frame
  • The number of just forward predircted macroblocks inside a B frame

  I would be very grateful for your help !

• Encoding and decoding timestamps per frame using libav* into mp4

  9 mai 2019, par Kevin

  I am writing a program for recording and playing back video together with another program that is connected to a piece of hardware we sell. This other program gathers data from hardware, which contains "timestamp" counters at a fixed sampling rate.

  I am looking for a way to encode these timestamps (either raw or converted to unix) into the outputted mp4 file. The main reason being that the video stream might only start getting saved a few minutes into the hardware acquisition

  Recording :

                  timestamp
  
  Main program --------------->  Video program
  
    |                                 |
  
    |                                 |
  
    v                                 v
  
  Save hardware data               Save frame data
  
    and timestamp                    and timestamp
  
  
  
    |                                 |
  
    |                                 |
  
    v                                 v
  
  Custom data format                .mp4 file

  Post processing analysis :

  for i in range(0,datalen):
  
      hardwareData, timestamp = readHardwareFile()
  
      frame, timestamp = readMP4()
  
  
  
      myData[timestamp].hardware = hardwareData
  
      mydata[timestamp].video = frame
  
  
  
  analyze(myData)

  The goal being that when a I want to playback in VLC, or with OpenCV, I have access to timestamps for each frame.

  I currently save it as a separate text file with timestamp and frame #, but I’m wondering if there is a more standardized way to do this.