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• libavcodec initialization to achieve real time playback with frame dropping when necessary

  20 octobre 2019, par Blake Senftner

  I have a C++ computer vision application linking with the ffmpeg libraries that provides frames from video streams to analysis routines. The idea being one can provide a moderately generic video stream identifier, and that video source will be decompressed and passed frame after frame to an analysis routine (which runs the user’s analysis functions.) The "moderately generic video identifier" covers 3 generic video stream types : paths to video files on disk, IP video streams (cameras or video streaming services), and USB webcam pins with desired format & rate.

  My current video player is generic as possible : video only, ignoring audio and other streams. It has a switch case for retrieving a stream’s frame rate based upon the stream’s source and codec, which is used to estimate the delay between decompressing frames. I’ve had many issues with trying to get reliable timestamps from the streams, so I am currently ignoring pts and dts. I know ignoring pts/dts is bad for variable frame rate streams. I plan to special case them later. The player currently checks to see if the last decompressed frame is more than 2 frames late (assuming a constant frame rate), and if so "drops the frame" - does not pass it to the user’s analysis routine.

  Essentially, the video player’s logic is determining when to skip frames (not pass them to the time consuming analysis routine) so the analysis is fed video frames in as close as possible to real time.

  I am looking for examples or discussions how one can initialize and/or maintain their AVFormatContext, AVStream, and AVCodecContext using (presumably but not limited to) AVDictionary options such that frame dropping as is necessary to maintain real time is performed at the libav libraries level, and not at my video player level. If achieving this requires separate AVDictionaies (or more) for each stream type and codec, then so be it. I am interested in understanding the pros and cons of both approachs : dropping frames at the player level or at the libav level.

  (When some analysis requires every frame, the existing player implementation with frame dropping disabled is fine. I suspect if I can get frame dropping to occur at the libav level, I’ll save the packet to frame decompression time as well, reducing the processing more than my current version.)

• How can I capture real time command line output of x265.exe with Python ?

  29 février 2020, par LeeRoermond

  I would like to write a GUI for x265.exe which presents a better (more humanized) real time progress .

  Here’s the code I used to capture subprocess’s output :

  import subprocess
  
  
  
  cmd = r'ping www.baidu.com -n 4'
  
  popen = subprocess.Popen(cmd, stdout = subprocess.PIPE ,stderr=subprocess.STDOUT ,shell=True)
  
  while True:
  
      next_line = popen.stdout.readline()
  
      if next_line == b'' and popen.poll() != None:
  
          break
  
      else:
  
          print(next_line.decode('ascii').replace('\r\n','\n') , end='')

  It performs perfectly with ’ping’.

  However ,when I swiched to ’x265’ command ,thing goes to wired.

  For example, If I replaced string variable 'cmd' into "x265 --y4m --crf 21 --output output.hevc input.y4m" in the preceding code.Theoretically , it should gives out the following output in lines arranged in order of time :

  y4m  [info]: 1920x1080 fps 24000/1001 i420p10 frames 0 - 100 of 101
  
  x265 [info]: Using preset ultrafast & tune none
  
  raw  [info]: output file: C:\temp\output.hevc
  
  x265 [info]: Main 10 profile, Level-4 (Main tier)
  
  x265 [info]: Thread pool created using 16 threads
  
  x265 [info]: Slices                              : 1
  
  x265 [info]: frame threads / pool features       : 4 / wpp(34 rows)
  
  x265 [info]: Coding QT: max CU size, min CU size : 32 / 16
  
  x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra
  
  x265 [info]: ME / range / subpel / merge         : dia / 57 / 0 / 2
  
  x265 [info]: Keyframe min / max / scenecut / bias: 23 / 250 / 0 / 5.00
  
  x265 [info]: Lookahead / bframes / badapt        : 5 / 3 / 0
  
  x265 [info]: AQ: mode / str / qg-size / cu-tree  : 1 / 0.0 / 32 / 1
  
  x265 [info]: Rate Control / qCompress            : CRF-21.0 / 0.60
  
  x265 [info]: tools: strong-intra-smoothing lslices=6 deblock
  
  
  
  [1.0%] 1/101 frames, 6.289 fps, 7217.8 kb/s
  
  [25.7%] 26/101 frames, 59.23 fps, 299.23 kb/s
  
  [45.5%] 46/101 frames, 66.76 fps, 322.81 kb/s  
  
  [69.3%] 70/101 frames, 73.30 fps, 224.53 kb/s
  
  [93.1%] 94/101 frames, 77.05 fps, 173.67 kb/s   
  
  
  
  x265 [info]: frame I:      1, Avg QP:23.45  kb/s: 7098.44 
  
  x265 [info]: frame P:     25, Avg QP:25.71  kb/s: 311.24  
  
  x265 [info]: frame B:     75, Avg QP:28.33  kb/s: 23.89   
  
  x265 [info]: consecutive B-frames: 3.8% 0.0% 0.0% 96.2% 
  
  
  
  encoded 101 frames in 1.22s (82.58 fps), 165.06 kb/s, Avg QP:27.64

  But the truth is, those output block in the middle part which indicates the real time progress will not be captured every specific it updated . popen.stdout.readline() command will be blocked until progress goes to 100% and then output altogether. Obviously that’s not what I want.

  ( ↓ I mean by this part)

  [1.0%] 1/101 frames, 6.289 fps, 7217.8 kb/s
  
  [25.7%] 26/101 frames, 59.23 fps, 299.23 kb/s
  
  [45.5%] 46/101 frames, 66.76 fps, 322.81 kb/s  
  
  [69.3%] 70/101 frames, 73.30 fps, 224.53 kb/s
  
  [93.1%] 94/101 frames, 77.05 fps, 173.67 kb/s   

  Could anyone help me fiture out what’s going on and how to fix it to achieve my goal ?

  Thanks a lot.

• Revision 64742f825d : Merge "Elevate NEWMV mode checking threshold in real time"

  2 juillet 2014, par Yunqing Wang

  Merge "Elevate NEWMV mode checking threshold in real time"