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• OpenCV (3.3.0) returns fail on VideoCapture with Video but works with Webcam [OS X]

  1er novembre 2017, par njoye

  Thanks for reading already, I’ve been trying to get this to work for a day and I didn’t get closer to the solution.

  I’m trying to get this object tracker to work. When I use a video from my webcam (with : python object-tracker-single.py -d 0, everything works as expected.

  But as soon as I’m trying to use a video file (i’ve tried different formats : .mp4, .mkv & .avi. I also tried to use the file given in the repository, that didn’t work as well. To see if there is a File not found-Error, I passed an invalid path to the function and an error got printed, that has not been printed when I used the other videos. So the file(s) i’m using is(/are) valid and not corrupted.

  I installed dlib through homebrew following this article and compiled OpenCV from the official source. This is the CMakeCache.txt that CMake spit out. After the first time I compiled it, I added opencv_contrib to the mix, thinking that it could help (I also think that I actually needed it), but that didn’t fix the problem.

  This is the code I’m having problems with :

  # Create the VideoCapture object
  
  cam = cv2.VideoCapture(source)
  
  
  
  # If Camera Device is not opened, exit the program
  
  if not cam.isOpened():
  
      print "Video device or file couldn't be opened"
  
      exit()
  
  
  
  print "Press key `p` to pause the video to start tracking"
  
  while True:
  
      # Retrieve an image and Display it.
  
      retval, img = cam.read() #<-- this returns false when trying to read a video 
  
      if not retval:
  
          print "Cannot capture frame device"
  
          exit()

  At the marked line, retval equals False and image equals None.
  It would already help me if I could somehow debug this behavior, but I didn’t find any way of doing so.

  I found that many Windows Users had problems with missing ffmpeg support, but that is not the case for me, since I used ffmpeg in previous (not OpenCV-related) projects and CMakeCache.txt reports that ffmpeg has been found and the compilation succeeded.

  I also tried using a fully qualified file-name for the video file, which either resulted in Video device or file couldn't be opened or the given problem.

  If you have any idea how this problem can be completely resolved, have an Idea on how to solve it or can provide me with a way of properly debugging this behavior, I’d be super glad to here it !

  Thanks already !

  -

  System : MacBook Pro (macOS Sierra 10.12.6)

  OpenCV Version : 3.3.0

  Dlib Version (not necessary imo, but hey) : 19.4.0

  Edit 2
  Output of cmake -DOPENCV_EXTRA_MODULES_PATH=../opencv_contrib-master/modules ../ >> result.txt : pastebin

• Can not add thumbnail image to MP4 using FFMPEG CLI

  5 novembre 2019, par Youssof H.

  After searching for hours, about the easiest solution for adding a thumbnail to an MP4 using a CLI, I came back to the start "FFMPEG". Though I skipped it at first wishing I will get a working tool but no, I will stick to "FFMPEG".

  Even after updating the repository ==> Same issue.

  I followed the exact code present at the official documentation that says :

  ffmpeg -i path/to/in.mp4 -i path/to/IMAGE.png -map 0 -map 1 -c copy -c:v:1 png -disposition:v:1 attached_pic path/to/out.mp4

  The following error log shows :

  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #0:1 -> #0:1 (copy)
  
    Stream #1:0 -> #0:2 (mjpeg (native) -> png (native))
  
  Press [q] to stop, [?] for help
  
  [swscaler @ 0x1fd0860] deprecated pixel format used, make sure you did set range correctly
  
  [swscaler @ 0x1fd0860] No accelerated colorspace conversion found from yuv420p to rgb24.
  
  [mp4 @ 0x1f747e0] track 1: codec frame size is not set
  
  [mp4 @ 0x1f747e0] opus in MP4 support is experimental, add '-strict -2' if you want to use it.
  
  Could not write header for output file #0 (incorrect codec parameters ?): Experimental feature
  
  Error initializing output stream 0:2 -- 
  
  Conversion failed!

  I have no idea how to fix this. I read the issues forum of the website but I did not find a similar issue. So I hope you guys will give a hand.

  Any suggested edits will be taken into consideration.

  Edit1 :

  Test1 : I brought an image(thumbnail) from the video itself and ran the command.

  Test2 : I brought a unique image(thumbnail) with different resolutions than the video yet the same error appears.

  ==>Useless

  Edit2 :

  First :

  After fixing my command to be like this
  ffmpeg -i path/to/in.mp4 -i path/to/IMAGE.png -map 0 -map 1 -c copy -c:v:1 png -disposition:v:1 attached_pic -strict -2 path/to/out.mp4
  I viewed the thumbnail using VLC (video player) so it showed up at first. But when I replaced the video and the thumbnail image with others I ran the command it runned smoothly, untill I viewed thumbnail again using VLC it showed the old thumbnail image it seemed to be cached somewhere during "FFMPEG" process. I had to delete the folder and make a new one in order to update the new thumbnail, but again it "caches" the first thumbnail used and shows it in VLC.

  Is it an issue from VLC or the "FFMPEG" is doing something weird ?

  Second :

  After I had the thumbnail showing up in VLC I wanted to test this feature by sending it to a contact on WhatsApp but it didn’t show. After a little search, I realized it might be connected to "og:image" metadata. Is there a way to edit this using CLI ?

  Third :

  Further, the video embedded with a thumbnail doesn’t play on Windows nor on iPhone nor on Android. When I open this using windows media player it says

  Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file.

  From here I think there is something I have to do with the codec.

  Note : the thumbnail shows in Windows File Explorer (but can not play video)

  Do you have any idea ?

• Naive Sorenson Video 1 Encoder

  12 septembre 2010, par Multimedia Mike — General

  (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

  At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

  Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.

  
  
  

  When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

  Level 5 blocks (mean-only 16×16 encoding) :
  

  
  
  

  Level 3 blocks (mean-only 8×8 encoding) :
  

  
  
  

  It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.

  
  
  

  Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.