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• Create a rolling X second webcam buffer in Linux, press button saves to file

  13 août 2016, par Grant Gibson

  I’m working on a webcam installation with an ’instant replay’ feature. The concept is basically this :

  1. Webcam captures live, 24/7
  2. When user presses a key, the last (previous) 30 seconds of video saves to a file
  3. I’ll then compress that video using something like FFMPEG and upload to a remote server

  I’m fine with step 3 and beyond, but I haven’t been able to find a solution that does the equivalent of a FIFO buffer for video streams [i.e. pretty much what the ’rewind live tv’ buffer on TiVo does].

  Does anyone know of a way to keep a rolling webcam video/audio buffer that can be exported to a file ?

  Design considerations :

  • I’m planning to use a standard webcam, but open to other suggestions
  • Recording would ideally be 1080p, 30fps
  • Recording must include sound
  • Linux hardware and OS can be specified in the answer, there are no existing pre-requisites. Raspberry Pi would be nice if that’s possible, but equally fine with a small Intel machine (e.g. NUC).
  • There’s no requirement to save the 24/7 stream, but it’s ok if that’s a by-product. So, storage permitting it can be saving to a file continuously for say 12 hours and just ’cat’ the last 30 secs to a separate file, if that’s an option ? But better would be the 30 sec rolling FIFO buffer that could potentially do the whole job in RAM.
  • The ’save instant replay’ button will eventually be a physical pushbutton rather than a keyboard key. However, I’ve got that side of things covered (if the solution is RPi I’d use the GPIO pins, if it’s an Intel box I’d probably use an Arduino in HID mode to simulate a keyboard press).

• Create webm from consecutive snapshots

  22 octobre 2014, par camb8

  How can I create a webm stream (to use with a video tag in a web application) from consecutive snapshots ? (on linux)

  I understand that I can do this be creating a streaming server using ffserver and providing a intup stream to the server (tutorial here) using ffmpeg.

  The snapshots can be obtained from a ip camera using it’s snapshot cgi (’http://ipaddress/snapshot.cgi’)

  I found this and this but both of them use files and not a url to provide input images.

• How to create a command – Introducing the Piwik Platform

  2 octobre 2014, par Thomas Steur — Development

  This is the next post of our blog series where we introduce the capabilities of the Piwik platform (our previous post was How to publish your plugin or theme on the Piwik Marketplace). This time you’ll learn how to create a new command. For this tutorial you will need to have basic knowledge of PHP.

  What is a command ?

  A command can execute any task on the command line. Piwik provides currently about 50 commands via the Piwik Console. These commands let you start the archiver, change the number of available custom variables, enable the developer mode, clear caches, run tests and more. You could write your own command to sync users or websites with another system for instance.

  Getting started

  In this series of posts, we assume that you have already set up your development environment. If not, visit the Piwik Developer Zone where you’ll find the tutorial Setting up Piwik.

  To summarize the things you have to do to get setup :

  • Install Piwik (for instance via git).
  • Activate the developer mode : ./console development:enable --full.
  • Generate a plugin : ./console generate:plugin --name="MyCommandPlugin". There should now be a folder plugins/MyCommandPlugin.
  • And activate the created plugin under Settings => Plugins.

  Let’s start creating a command

  We start by using the Piwik Console to create a new command. As you can see there is even a command that lets you easily create a new command :

  ./console generate:command

  The command will ask you to enter the name of the plugin the created command should belong to. I will simply use the above chosen plugin name “MyCommandPlugin”. It will ask you for a command name as well. I will use “SyncUsers” in this example. There should now be a file plugins/MyCommandPlugin/Commands/Syncusers.php which contains already an example to get you started easily :

  class Syncusers extends ConsoleCommand
  {
      protected function configure()
      {
          $this->setName('mycommandplugin:syncusers');
          $this->setDescription('MyCommandPlugin');
          $this->addOption('name', null, InputOption::VALUE_REQUIRED, 'Your name:');
      }
   
      /**
       * Execute command like: ./console mycommandplugin:syncusers --name="The Piwik Team"
       */
      protected function execute(InputInterface $input, OutputInterface $output)
      {
          $name    = $input->getOption('name');
   
          $message = sprintf('Syncusers: %s', $name);
   
          $output->writeln($message);
      }
  }
  Télécharger

  Any command that is placed in the “Commands” folder of your plugin will be available on the command line automatically. Therefore, the newly created command can now be executed via ./console mycommandplugin:syncusers --name="The Piwik Team".

  The code template explained

  protected function configure()
  {
      $this->setName('mycommandplugin:checkdatabase');
      $this->setDescription('MyCommandPlugin');
      $this->addOption('name', null, InputOption::VALUE_REQUIRED, 'Your name:');
  }
  Télécharger

  As the name says the method configure lets you configure your command. You can define the name and description of your command as well as all the options and arguments you expect when executing it.

  protected function execute(InputInterface $input, OutputInterface $output)
  {
      $name    = $input->getOption('name');
      $message = sprintf('Syncusers: %s', $name);
      $output->writeln($message);
  }
  Télécharger

  The actual task is defined in the execute method. There you can access any option or argument that was defined on the command line via $input and write anything to the console via $output argument.

  In case anything went wrong during the execution you should throw an exception to make sure the user will get a useful error message. Throwing an exception when an error occurs will make sure the command does exit with a status code different than 0 which can sometimes be important.

  Advanced features

  The Piwik Console is based on the powerful Symfony Console component. For instance you can ask a user for any interactive input, you can use different output color schemes and much more. If you are interested in learning more all those features have a look at the Symfony console website.

  How to test a command

  After you have created a command you are surely wondering how to test it. Ideally, the actual command is quite short as it acts like a controller. It should only receive the input values, execute the task by calling a method of another class and output any useful information. This allows you to easily create a unit or integration test for the classes behind the command. We will cover this topic in one of our future blog posts. Just one hint : You can use another command ./console generate:test to create a test. If you want to know how to test a command have a look at the Testing Commands documentation.

  Publishing your Plugin on the Marketplace

  In case you want to share your commands with other Piwik users you can do this by pushing your plugin to a public GitHub repository and creating a tag. Easy as that. Read more about how to distribute a plugin and best practices when publishing a plugin.

  Isn’t it easy to create a command ? We never even created a file ! If you have any feedback regarding our APIs or our guides in the Developer Zone feel free to send it to us.