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• GStreamer : cannot link elements

  9 septembre 2018, par Han Jingyu

  when rosruning my own project, I got an unexpected error as below
  I was guessing it was caused by some problems encountered in the process of installing OpenCV.So I reinstalled and recompiled the opencv, but this error still exists.
  then I noticed the message, GStreamer : cannot link elements. I was thinking it probably related to GStreamer. Unfortunately, I don’t know how to fix this problem. little clues would be appreciated.

  ** (ros_exploration:14898): CRITICAL **: gst_missing_encoder_message_new: assertion 'gst_caps_is_fixed (encode_caps)' failed         
  
    (ros_exploration:14898): GStreamer-CRITICAL **: gst_element_post_message: assertion 'message != NULL' failed
  
      OpenCV Error: Unspecified error (GStreamer: cannot link elements        
  
          ) in CvVideoWriter_GStreamer::open, file /home/htf/Downloads/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp, line 1464
  
      Qt has caught an exception thrown from an event handler. Throwing
  
      exceptions from an event handler is not supported in Qt. You must
  
      reimplement QApplication::notify() and catch all exceptions there.
  
      terminate called after throwing an instance of 'cv::Exception'
  
        what():  /home/htf/Downloads/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp:1464: error: (-2) GStreamer: cannot link elements
  
       in function CvVideoWriter_GStreamer::open
  
  
  
     Aborted (core dumped)

• Getting Audio and Video from Steams

  16 novembre 2018, par anon

  I’m trying to download a video from BritBox. After observing my network packets, it seems they stream the video in .m4s fragments.

  I’ve looked into InviDownloader, but can’t seem to get it to pick up all the pieces. I don’t think I’m giving it the correct URL but can’t find the correct one either. I’ve taken a look at this question but I think it requires a specific URL as well, which I can’t seem to find.

  Most fragments (if not all) have a .dash extension, so I tried to get it working with GPAC’s dashcast but couldn’t get that working either. I’ve also seen Handbrake being thrown around but haven’t tried it.

  After trying tons of browser extensions, I found one that can correctly piece together the .m4s files, at least to an extent. If you carefully refresh the extension when new packets are downloaded, you can download a result of the entire .m4s.

  Then, using youtube-dl and ffmpeg you can convert it to an mp4 file. However, this has no audio.

  I’m not too savvy when it comes to videos or streaming. Is there an easy way to download these videos to an mp4 format with audio ?

• A Better Process Runner

  1er janvier 2011, par Multimedia Mike — Python

  I was recently processing a huge corpus of data. It went like this : For each file in a large set, run 'cmdline-tool <file>', capture the output and log results to a database, including whether the tool crashed. I wrote it in Python. I have done this exact type of the thing enough times in Python that I’m starting to notice a pattern.

  Every time I start writing such a program, I always begin with using Python’s commands module because it’s the easiest thing to do. Then I always have to abandon the module when I remember the hard way that whatever ’cmdline-tool’ is, it might run errant and try to execute forever. That’s when I import (rather, copy over) my process runner from FATE, the one that is able to kill a process after it has been running too long. I have used this module enough times that I wonder if I should spin it off into a new Python module.

  Or maybe I’m going about this the wrong way. Perhaps when the data set reaches a certain size, I’m really supposed to throw it on some kind of distributed cluster rather than task it to a Python script (a multithreaded one, to be sure, but one that runs on a single machine). Running the job on a distributed architecture wouldn’t obviate the need for such early termination. But hopefully, such architectures already have that functionality built in. It’s something to research in the new year.

  I guess there are also process limits, enforced by the shell. I don’t think I have ever gotten those to work correctly, though.