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• LibVLC : Retrieving current frame number

  2 avril 2015, par Solidus

  I am doing a project which involves a bit of video recording and editing and I am struggling to find a good C++ library to use. I am using QT as my framework and their video player is not working properly for me to use (seeking crashes some times, e.g.). Also, I need to record video and audio from my camera and QCamera does not work in windows (for recording).

  On my program the user can draw on top of the video and I need to store the start frame and the end frame of those drawings.

  Right now I’ve been testing Libvlc which almost does what I want. From what I can see they don’t have a way to just jump to a certain frame as this can only be done by time or position.

  The first solution that I came up with was to capture the time change event and then calculate the frame using the FPS. The problem is that, as far as I can tell, the interval of this event is around 250ms, which for a 15fps video is almost 4 frames.

  So, the second solution was to use libvlc_video_set_callbacks to make my own "lock, unlock and display" and count the frames there. This works for recording from the camera, as there is no going back and the frames go from 0 until the video stops. The problem is when playing a video. Since there is no timestamp, as far as I can tell, there is no way for me to know in which frame number I am (the user can be seeking for example). My "hacky" solution was to have a "lastTime" and "numTimes" on the struct I pass into these callbacks and this is what I do :

  lastTime represents the "last new time" received and numTimes represents the number of times lastTime was received.

  get_the_current_time
  
  calculate_frame_num_with_fps
  
  if current_time is equal to lastTime: 
  
       frameNum += numTimes
  
       numTimes++
  
  else 
  
       lastTime = current_time
  
       numTimes = 1

  This kinda works but I hate the solution. I’m not sure if when doing seeking the time changes if the difference is less than 250ms. That would maybe be kinda hard for a user to do but I’d prefer not to implement it like that.

  So my question is if there is another solution for this ? If not, any libraries that could help me on this ? I know about FFMPEG which seems would solve me this problem as it’s more low level and I could implement this solution. The problem is my deadline is approaching and that would still me take some time (learning the library and doing all the work). So I was thinking of it as a last resort.

  Thank you for your time.

• Retrieving current frame number

  2 avril 2015, par Solidus

  I am doing a project which involves a bit of video recording and editing and I am struggling to find a good C++ library to use. I am using QT as my framework and their video player is not working properly for me to use (seeking crashes some times, e.g.). Also, I need to record video and audio from my camera and QCamera does not work in windows (for recording).

  On my program the user can draw on top of the video and I need to store the start frame and the end frame of those drawings.

  Right now I’ve been testing Libvlc which almost does what I want. From what I can see they don’t have a way to just jump to a certain frame as this can only be done by time or position.

  The first solution that I came up with was to capture the time change event and then calculate the frame using the FPS. The problem is that, as far as I can tell, the interval of this event is around 250ms, which for a 15fps video is almost 4 frames.

  So, the second solution was to use libvlc_video_set_callbacks to make my own "lock, unlock and display" and count the frames there. This works for recording from the camera, as there is no going back and the frames go from 0 until the video stops. The problem is when playing a video. Since there is no timestamp, as far as I can tell, there is no way for me to know in which frame number I am (the user can be seeking for example). My "hacky" solution was to have a "lastTime" and "numTimes" on the struct I pass into these callbacks and this is what I do :

  lastTime represents the "last new time" received and numTimes represents the number of times lastTime was received.

  get_the_current_time
  
  calculate_frame_num_with_fps
  
  if current_time is equal to lastTime: 
  
       frameNum += numTimes
  
       numTimes++
  
  else 
  
       lastTime = current_time
  
       numTimes = 1

  This kinda works but I hate the solution. I’m not sure if when doing seeking the time changes if the difference is less than 250ms. That would maybe be kinda hard for a user to do but I’d prefer not to implement it like that.

  So my question is if there is another solution for this ? If not, any libraries that could help me on this ? I know about FFMPEG which seems would solve me this problem as it’s more low level and I could implement this solution. The problem is my deadline is approaching and that would still me take some time (learning the library and doing all the work). So I was thinking of it as a last resort.

  Thank you for your time.

• Android, fast video processing

  27 avril 2016, par Ilja Kosynkin

  I have troubles in my current project which requires video processing. Basically crop function (video should be squared), trimming (video shouldn’t be longer than 30 seconds) and quality reduction (bitrate should be equal 713K).
  I’ve succesfully embedded FFmpeg into application, all functions are working quite fine except one major detail - processing as per my boss is taking too long time. For video that have around 52 MB for 36 seconds it’s taking 50 seconds to perforn all the operations (I’m trimming video to 30 seconds before any other operation obviously). The problem is that on parallel project on iOS video processing takes like 10-15 seconds for greater files. I assume that it’s related to fact that they’re using Apple QuickTime format which obviusly was developed by Apple so it’s not surprising that it’s working quite fast.
  So well, it was introduction, now my question : is there any way for Android to process any video in any quality (for now we can assume that all videos are in h264) in time of 10-15 seconds (not more then in 30 seconds, as my boss said) ? Some alternative to FFmpeg, that can perform operations faster ? I’nm pretty sure that there is no possibility to perform such work in a such short time, since I already feel like I searched thought while Internet, but I want to make sure that there is really no possibility to do such work. If anyone can provide me links to solution more faster than FFmpeg or confirm that there is no such solution, I will be very gratefull.

  Update
  Thanks to Alex Cohn I’ve resolved this with MediaCodec. After a while, I got 20 seconds processing on 52MB video with cropping to square and lowering bitrate. For any future Googlers out of here I can suggest to take a look at this respository :
  Many stuff about MediaCodec
  and more precisely at this file : Extract, edit and encode again, video and audio