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• Introducing the Piwik Java Tracker – Analytics for your Java based applications

  18 novembre 2015, par Brett — Community, Development

  Hello Piwik Community !

  My name is Brett Csorba, a Software Engineer out of the US. I’d like to introduce the Piwik Java Tracker project, an easy way to track usage data within your Java applications !

  When would I need to track users in a Java application ? What’s wrong with front end tracking ?

  Absolutely nothing ! We encourage users to track information where it makes the most sense for them ! But in cases where

  • you have a 100% Java based application
  • you expose a REST layer where users can bypass your front end tracking code
  • you have valuable data you want to track that is unnecessary or too sensitive to pass back to the user

  the Piwik Java Tracker can help you track the data you need.

  What exactly can it track ?

  We aim to provide the full Tracking HTTP API. If you find we’ve left something out by mistake, let us know !

  You’ve sparked my curiosity, how would I use such a thing ?

  Well, once you’ve installed Piwik and set up your first website, you can grab the latest jar and include it in your project. The dependencies needed to both use and test this library can be found here.

  This library is intended to be used for projects that support Java 8. The released binaries are built, tested, and deployed from Oracle JDK 8.

  Using this API is as simple as creating a new request

  PiwikRequest request = new PiwikRequest(1, new URL("http://my-site.com/action")) ;

  Setting some more information if you want to

  request.setActionName("myAction") ;
  request.setPageCustomVariable("key", "value") ;

  and firing the request.

  PiwikTracker tracker = new PiwikTracker("http://your-piwik-domain.tld/piwik.php") ;
  HttpResponse response = tracker.sendRequest(request) ;

  Check out this guide to using the API for some more information !

  Looks cool so far, can I help out ?

  Yes ! Absolutely ! Download the project, try it, break it without mercy ! (Just make sure you tell us how.) Contribute to the project or let us know what we can do to it to improve it. As with all open source projects, we need your help to improve it.

• How to Simply Remove Duplicate Frames from a Video using ffmpeg

  29 janvier 2017, par Skeeve

  First of all, I’d preface this by saying I’m NO EXPERT with video manipulation,
  although I’ve been fiddling with ffmpeg for years (in a fairly limited way). Hence, I’m not too flash with all the language folk often use... and how it affects what I’m trying to do in my manipulations... but I’ll have a go with this anyway...

  I’ve checked a few links here, for example :
  ffmpeg - remove sequentially duplicate frames

  ...but the content didn’t really help me.

  I have some hundreds of video clips that have been created under both Windows and Linux using both ffmpeg and other similar applications. However, they have some problems with times in the video where the display is ’motionless’.

  As an example, let’s say we have some web site that streams a live video into, say, a Flash video player/plugin in a web browser. In this case, we’re talking about a traffic camera video stream, for example.

  There’s an instance of ffmpeg running that is capturing a region of the (Windows) desktop into a video file, viz :-

  ffmpeg -hide_banner -y -f dshow ^
  
        -i video="screen-capture-recorder" ^
  
        -vf "setpts=1.00*PTS,crop=448:336:620:360" ^
  
        -an -r 25 -vcodec libx264 -crf 0 -qp 0 ^
  
        -preset ultrafast SAMPLE.flv

  Let’s say the actual ’display’ that is being captured looks like this :-

  123456789 XXXXX 1234567 XXXXXXXXXXX 123456789 XXXXXXX
  
  ^---a---^ ^-P-^ ^--b--^ ^----Q----^ ^---c---^ ^--R--^ 

  ...where each character position represents a (sequence of) frame(s). Owing to a poor internet connection, a "single frame" can be displayed for an extended period (the ’X’ characters being an (almost) exact copy of the immediately previous frame). So this means we have segments of the captured video where the image doesn’t change at all (to the naked eye, anyway).

  How can we deal with the duplicate frames ?... and how does our approach change if the ’duplicates’ are NOT the same to ffmpeg but LOOK more-or-less the same to the viewer ?

  If we simply remove the duplicate frames, the ’pacing’ of the video is lost, and what used to take, maybe, 5 seconds to display, now takes a fraction of a second, giving a very jerky, unnatural motion, although there are no duplicate images in the video. This seems to be achievable using ffmpeg with an ’mp_decimate’ option, viz :-

       ffmpeg -i SAMPLE.flv ^                      ... (i)
  
          -r 25 ^
  
          -vf mpdecimate,setpts=N/FRAME_RATE/TB DEC_SAMPLE.mp4

  That reference I quoted uses a command that shows which frames ’mp_decimate’ will remove when it considers them to be ’the same’, viz :-

       ffmpeg -i SAMPLE.flv ^                      ... (ii)
  
          -vf mpdecimate ^
  
          -loglevel debug -f null -

  ...but knowing that (complicated formatted) information, how can we re-organize the video without executing multiple runs of ffmpeg to extract ’slices’ of video for re-combining later ?

  In that case, I’m guessing we’d have to run something like :-

  • user specifies a ’threshold duration’ for the duplicates
    (maybe run for 1 sec only)
  • determine & save main video information (fps, etc - assuming
    constant frame rate)
  • map the (frame/time where duplicates start)->no. of
    frames/duration of duplicates
  • if the duration of duplicates is less than the user threshold,
    don’t consider this period as a ’series of duplicate frames’
    and move on
  • extract the ’non-duplicate’ video segments (a, b & c in the
    diagram above)
  • create ’new video’ (empty) with original video’s specs
  • for each video segment
    extract the last frame of the segment
    create a short video clip with repeated frames of the frame
    just extracted (duration = user spec. = 1 sec)
    append (current video segment+short clip) to ’new video’
    and repeat

  ...but in my case, a lot of the captured videos might be 30 minutes long and have hundreds of 10 sec long pauses, so the ’rebuilding’ of the videos will take a long time using this method.

  This is why I’m hoping there’s some "reliable" and "more intelligent" way to use
  ffmepg (with/without the ’mp_decimate’ filter) to do the ’decimate’ function in only a couple of passes or so... Maybe there’s a way that the required segments could even be specified (in a text file, for example) and as ffmpeg runs it will
  stop/restart it’s transcoding at specified times/frame numbers ?

  Short of this, is there another application (for use on Windows or Linux) that could do what I’m looking for, without having to manually set start/stop points,
  extracting/combining video segments manually...?

  I’ve been trying to do all this with ffmpeg N-79824-gcaee88d under Win7-SP1 and (a different version I don’t currently remember) under Puppy Linux Slacko 5.6.4.

  Thanks a heap for any clues.

• Dreamcast Track Sizes

  1er mars 2015, par Multimedia Mike — Sega Dreamcast

  I’ve been playing around with Sega Dreamcast discs lately. Not playing the games on the DC discs, of course, just studying their structure. To review, the Sega Dreamcast game console used special optical discs named GD-ROMs, where the GD stands for “gigadisc”. They are capable of holding about 1 gigabyte of data.

  You know what’s weird about these discs ? Each one manages to actually store a gigabyte of data. Each disc has a CD portion and a GD portion. The CD portion occupies the first 45000 sectors and can be read in any standard CD drive. This area is divided between a brief data track and a brief (usually) audio track.

  The GD region starts at sector 45000. Sometimes, it’s just one humongous data track that consumes the entire GD region. More often, however, the data track is split between the first track and the last track in the region and there are 1 or more audio tracks in between. But the weird thing is, the GD region is always full. I made a study of it (click for a larger, interactive graph) :

  
  
  

  Some discs put special data or audio bonuses in the CD region for players to discover. But every disc manages to fill out the GD region. I checked up on a lot of those audio tracks that divide the GD data and they’re legitimate music tracks. So what’s the motivation ? Why would the data track be split in 2 pieces like that ?

  I eventually realized that I probably answered this question in this blog post from 4 years ago. The read speed from the outside of an optical disc is higher than the inside of the same disc. When I inspect the outer data tracks of some of these discs, sure enough, there seem to be timing-sensitive multimedia FMV files living on the outer stretches.

  One day, I’ll write a utility to take apart the split ISO-9660 filesystem offset from a weird sector.