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• FFMPEG : Extracting 20 images from a video of variable length

  12 novembre 2013, par Vapire

  I've browsed the internet for this very intensively, but I didn't find what I needed, only variations of it which are not quite the thing I want to use.

  I've got several videos in different lengths and I want to extract 20 images out of every video from start to the end, to show the broadest impression of the video.

  So one video is 16m 47s long => 1007s in total => I have to make one snapshot of the video every 50 seconds.

  So I figured using the -r switch of ffmpeg with the value of 0.019860973 (eq 20/1007) but ffmpeg tells me that the framerate is too small for it...

  The only way I figured out to do it would be to write a script which calls ffmpeg with a manipulated -ss switch and using -vframes 1 but this is quite slow and a little bit off for me since ffmpegs numerates the images itself...

  Any suggestions or directions ?

  Thanks,
  Vapire

• Find video resolution and video duration of remote mediafile

  22 février 2012, par osgx

  I want to write an program which can find some metainformation of mediafile. I'm interested in popular video formats, such as avi, mkv, mp4, mov (may be other popular too). I want basically to get :

  • Video size (720, 1080, 360 etc)
  • Total runtime of video (may be not very exact)
  • Number of audio streams
  • Name of video codec
  • Name of audio codec

  There is already the mediainfo, but in my program I want to get information about remote file, which may be accessed via ftp, http, samba ; or even torrent (there are some torrent solutions, which allows to read not-yet downloaded file).

  MediaInfo library have no support of samba (smb ://) and mkv format (for runtime).

  Also, I want to know, how much data should be downloaded to get this information. I want not to download full videofile because I have no enough disk space.

  Is this information in the first 1 or 10 or 100 KiloBytes of the file ? Is it at predictable offset if I know the container name and total file size ?

  PS : Platform is Linux, Language is C/C++

• ffmpeg c/c++ get frame count or timestamp and fps

  23 juin 2016, par broschb

  I am using ffmpeg to decode a video file in C. I am struggling to get either the count of the current frame I am decoding or the timestamp of the frame. I have read numerous posts that show how to calculate an estimated frame no based on the fps and frame timestamp, however I am not able to get either of those.

  What I need : fps of video file, timestamp of current frame or frame no(not calculated)

  What I have : I am able to get the time of the video using

  pFormatCtx->duration/AV_TIME_BASE

  I am counting the frames currently as I process them, and getting a current frame count, this is not going to work longterm though. I can get the total frame count for the file using

  pFormatCtx->streams[currentStream->videoStream]->nb_frames

  I have read this may not work for all streams, although it has worked for every stream I have tried.

  I have tried using the time_base.num and time_base.den values and packet.pts, but I can’t make any sense of the values that I am getting from those, so I may just need to understand better what those values are.

  Does anyone know of resources that show examples on how to get this values ?