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• On ALAC’s Open Sourcing

  1er novembre 2011, par Multimedia Mike — Codec Technology

  Apple open sourced their lossless audio codec last week. Pretty awesome ! I have a theory that, given enough time, absolutely every codec will be open source in one way or another.

  I know I shouldn’t bother reading internet conversation around any news related to multimedia technology. And if I do read it, I shouldn’t waste any effort getting annoyed about them. But here are some general corrections :

  • ALAC is not in the same league as — nor is it a suitable replacement for — MP3/AAC/Vorbis or any other commonly used perceptual audio codec. It’s not a matter of better or worse ; they’re just different families of codecs designed for different purposes.
  • Apple open sourced ALAC, not AAC– easy mistake, though there’s nothing to ‘open source’ about AAC (though people can, and will, argue about its absolute ‘open-ness’).
  • There’s not much technical room to argue between ALAC and FLAC, the leading open source lossless audio compressor. Both perform similarly in terms of codec speeds (screamingly fast) and compression efficiency (results vary slightly depending on source material).
  • Perhaps the most frustrating facet is the blithe ignorance about ALAC’s current open source status. While this event simply added an official “open source” status to the codec, ALAC has effectively been open source for a very long time. According to my notes, the ALAC decoding algorithm was reverse engineered in 2005 and added into FFmpeg in March of the same year. Then in 2008, Google — through their Summer of Code program — sponsored an open source ALAC encoder.

  From the multimedia-savvy who are versed in these concepts, the conversation revolves around which would win in a fight, ALAC or FLAC ? And who between Apple and FFmpeg/Libav has a faster ALAC decoder ? The faster and more efficient ALAC encoder ? I contend that these issues don’t really matter. If you have any experience working with lossless audio encoders, you know that they tend to be ridiculously fast to both encode and decode and that many different lossless codecs compress at roughly the same ratios.

  As for which encoder is the fastest : use whatever encoder is handiest and most familiar, either iTunes or FFmpeg/Libav.

  As for whether to use FLAC or ALAC — if you’ve already been using one or the other for years, keep on using it. Support isn’t going to vanish. If you’re deciding which to use for a new project, again, perhaps choose based on software you’re already familiar with. Also, consider hardware support– ALAC enjoys iPod support, FLAC is probably better supported in a variety of non-iPod devices, though that may change going forward due to this open sourcing event.

  For my part, I’m just ecstatic that the question of moral superiority based on open source status has been removed from the equation.

  Code-wise, I’m interested in studying the official ALAC code to see if it has any corner-case modes that the existing open source decoders don’t yet account for. The source makes mention of multichannel (i.e., greater than stereo) configurations, but I don’t know if that’s in FFmpeg/Libav.

• Open USB camera with OpenCV and stream to rtsp server

  12 septembre 2017, par user2594166

  I got a Logitech C920 camera connected via USB to a NVIDIA TX1. I am trying to both stream the camera feed over rtsp to a server while doing some computer vision in OpenCV. I managed to read H264 video from the usb camera in Opencv

  #include <iostream>
  
  #include "opencv/cv.h"
  
  #include <opencv2></opencv2>opencv.hpp>
  
  #include "opencv/highgui.h"
  
  
  
  using namespace cv;
  
  using namespace std;
  
  
  
  int main()
  
  {
  
      Mat img;
  
      VideoCapture cap;
  
      int heightCamera = 720;
  
      int widthCamera = 1280;
  
  
  
      // Start video capture port 0
  
      cap.open(0);
  
  
  
  
  
      // Check if we succeeded
  
      if (!cap.isOpened())
  
      {
  
          cout &lt;&lt; "Unable to open camera" &lt;&lt; endl;
  
          return -1;
  
      }
  
      // Set frame width and height
  
      cap.set(CV_CAP_PROP_FRAME_WIDTH, widthCamera);
  
      cap.set(CV_CAP_PROP_FRAME_HEIGHT, heightCamera);
  
      cap.set(CV_CAP_PROP_FOURCC, CV_FOURCC('X','2','6','4'));
  
  
  
      // Set camera FPS
  
      cap.set(CV_CAP_PROP_FPS, 30);
  
  
  
      while (true)
  
      {
  
          // Copy the current frame to an image
  
          cap >> img;
  
  
  
          // Show video streams
  
          imshow("Video stream", img);
  
  
  
          waitKey(1);
  
      }
  
  
  
      // Release video stream
  
      cap.release();
  
  
  
      return 0;
  
  }
  
  </iostream>

  I also have streamed the USB camera to a rtsp server by using ffmpeg :
  ffmpeg -f v4l2 -input_format h264 -timestamps abs -video_size hd720 -i /dev/video0 -c:v copy -c:a none -f rtsp rtsp://10.52.9.104:45002/cameraTx1

  I tried to google how to combine this two functions, i.e. open usb camera in openCV and use openCV to stream H264 rtsp video. However, all I can find is people trying to open rtsp stream in openCV.

  Have anyone successfully stream H264 rtsp video using openCV with ffmpeg ?

  Best regards
  Sondre

• Changes to the WebM Open Source License

  4 juin 2010, par noreply@blogger.com (John Luther)

  You’ll see on the WebM license page and in our source code repositories that we’ve made a small change to our open source license. There were a couple of issues that popped up after we released WebM at Google I/O a couple weeks ago, specifically around how the patent clause was written.

  As it was originally written, if a patent action was brought against Google, the patent license terminated. This provision itself is not unusual in an OSS license, and similar provisions exist in the 2nd Apache License and in version 3 of the GPL. The twist was that ours terminated "any" rights and not just rights to the patents, which made our license GPLv3 and GPLv2 incompatible. Also, in doing this, we effectively created a potentially new open source copyright license, something we are loath to do.

  Using patent language borrowed from both the Apache and GPLv3 patent clauses, in this new iteration of the patent clause we’ve decoupled patents from copyright, thus preserving the pure BSD nature of the copyright license. This means we are no longer creating a new open source copyright license, and the patent grant can exist on its own. Additionally, we have updated the patent grant language to make it clearer that the grant includes the right to modify the code and give it to others. (We’ve updated the licensing FAQ to reflect these changes as well.)

  We’ve also added a definition for the "this implementation" language, to make that more clear.

  Thanks for your patience as we worked through this, and we hope you like, enjoy and (most importantly) use WebM and join with us in creating more freedom online. We had a lot of help on these changes, so thanks to our friends in open source and free software who traded many emails, often at odd hours, with us.

  Chris DiBona is the Open Source Programs Manager at Google.