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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.)

• avutil/avstring : support input path as a null pointer or empty string

  24 septembre 2019, par Limin Wang

  avutil/avstring : support input path as a null pointer or empty string
  Linux and OSX systems support basename and dirname via <libgen.h>, I plan to
  
  make the wrapper interface conform to the standard interface first.
  
  If it is feasible, I will continue to modify it to call the system interface
  
  if there is already a system call interface.
  You can get more description about the system interface by below command :
  
   "man 3 basename"
  Reviewed-by : Marton Balint <cus@passwd.hu>
  
  Reviewed-by : Tomas Härdin <tjoppen@acc.umu.se>
  
  Reviewed-by : Steven Liu <lq@chinaffmpeg.org>
  
  Signed-off-by : Limin Wang <lance.lmwang@gmail.com>
  

  • [DH] libavutil/avstring.c
  • [DH] libavutil/avstring.h

• Bat file that extracts subtitle file then hard encodes the subtitle file into the original mkv file

  1er septembre 2019, par NolanWinsman

  My tv can play mkv files off of a flash drive but it cannot detect the subtitles files. I am trying to make a bat file that essentially takes the .srt file out of the mkv file then hard encodes it into the mkv file using ffmpeg. I am getting close but the naming is not working properly. For instance when it creates the subtitle file it names it infile.mkv.srt. When the file is encoded it is named infile.mkvEncoded.mkv. I am trying to get rid of the extra .mkv

  I am not great with variables in bat files so I am not exactly sure what to do. I added the "Encoded" part to the name of the file so that it doesn’t overwrite the original infile. I plan on just using bulk rename utility to get rid of that part unless there is a better way.

  My code is :

      DO (
  
      MKDIR Encoded_Files
  
      )
  
      FOR /F "tokens=*" %%G IN ('dir /b *.mkv') DO (
  
          ffmpeg -i "%%G" -vn -an -codec:s:0.1 srt "%%G.srt"
  
          ffmpeg -i "%%G" -vf "subtitles=%%G.srt" "%%GConverted"
  
          move *"%%~nG" "Encoded_Files"
  
              )

  The expected result would be infileEncoded.mkv*