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• Grand Unified Theory of Compact Disc

  1er février 2013, par Multimedia Mike — General

  This is something I started writing about a decade ago (and I almost certainly have some of it wrong), back when compact discs still had a fair amount of relevance. Back around 2002, after a few years investigating multimedia technology, I took an interest in compact discs of all sorts. Even though there may seem to be a wide range of CD types, I generally found that they’re all fundamentally the same. I thought I would finally publishing something, incomplete though it may be.

  Physical Perspective
  There are a lot of ways to look at a compact disc. First, there’s the physical format, where a laser detects where pits/grooves have disturbed the smooth surface (a.k.a. lands). A lot of technical descriptions claim that these lands and pits on a CD correspond to ones and zeros. That’s not actually true, but you have to decide what level of abstraction you care about, and that abstraction is good enough if you only care about the discs from a software perspective.

  Grand Unified Theory (Software Perspective)
  Looking at a disc from a software perspective, I have generally found it useful to view a CD as a combination of a 2 main components :

  • table of contents (TOC)
  • a long string of sectors, each of which is 2352 bytes long

  I like to believe that’s pretty much all there is to it. All of the information on a CD is stored as a string of sectors that might be chopped up into a series of anywhere from 1-99 individual tracks. The exact sector locations where these individual tracks begin are defined in the TOC.

  Audio CDs (CD-DA / Red Book)
  The initial purpose for the compact disc was to store digital audio. The strange sector size of 2352 bytes is an artifact of this original charter. “CD quality audio”, as any multimedia nerd knows, is formally defined as stereo PCM samples that are each 16 bits wide and played at a frequency of 44100 Hz.
  

  (44100 audio frames / 1 second) * (2 samples / audio frame) * 
    (16 bits / 1 sample) * (1 byte / 8 bits) = 176,400 bytes / second
  (176,400 bytes / 1 second) / (2352 bytes / 1 sector) = 75
  

  75 is the number of sectors required to store a single second of CD-quality audio. A single sector stores 1/75th of a second, or a ‘frame’ of audio (though I think ‘frame’ gets tossed around at all levels when describing CD formats).

  The term “red book” is thrown around in relation to audio CDs. There is a series of rainbow books that define various optical disc standards and the red book describes audio CDs.

  Basic Data CD-ROMs (Mode 1 / Yellow Book)
  Somewhere along the line, someone decided that general digital information could be stored on these discs. Hence, the CD-ROM was born. The standard model above still applies– TOC and string of 2352-byte sectors. However, it’s generally only useful to have a single track on a CD-ROM. Thus, the TOC only lists a single track. That single track can easily span the entire disc (something that would be unusual for a typical audio CD).

  While the model is mostly the same, the most notable difference between and audio CD and a plain CD-ROM is that, while each sector is 2352 bytes long, only 2048 bytes are used to store actual data payload. The remaining bytes are used for synchronization and additional error detection/correction.

  At least, the foregoing is true for mode 1 / form 1 CD-ROMs (which are the most common). “Mode 1″ CD-ROMs are defined by a publication called the yellow book. There is also mode 1 / form 2. This forgoes the additional error detection and correction afforded by form 1 and dedicates 2336 of the 2352 sector bytes to the data payload.

  CD-ROM XA (Mode 2 / Green Book)
  From a software perspective, these are similar to mode 1 CD-ROMs. There are also 2 forms here. The first form gives a 2048-byte data payload while the second form yields a 2324-byte data payload.

  Video CD (VCD / White Book)
  These are CD-ROM XA discs that carry MPEG-1 video and audio data.

  Photo CD (Beige Book)
  This is something I have never personally dealt with. But it’s supposed to conform to the CD-ROM XA standard and probably fits into my model. It seems to date back to early in the CD-ROM era when CDs were particularly cost prohibitive.

  Multisession CDs (Blue Book)
  Okay, I admit that this confuses me a bit. Multisession discs allow a user to burn multiple sessions to a single recordable disc. I.e., burn a lump of data, then burn another lump at a later time, and the final result will look like all the lumps were recorded as the same big lump. I remember this being incredibly useful and cost effective back when recordable CDs cost around US$10 each (vs. being able to buy a spindle of 100 CD-Rs for US$10 or less now). Studying the cdrom.h file for the Linux OS, I found a system call named CDROMMULTISESSION that returns the sector address of the start of the last session. If I were to hypothesize about how to make this fit into my model, I might guess that the TOC has some hint that the disc was recorded in multisession (which needs to be decided up front) and the CDROMMULTISESSION call is made to find the last session. Or it could be that a disc read initialization operation always leads off with the CDROMMULTISESSION query in order to determine this.

  I suppose I could figure out how to create a multisession disc with modern software, or possibly dig up a multisession disc from 15+ years ago, and then figure out how it should be read.

  CD-i
  This type puzzles my as well. I do have some CD-i discs and I thought that I could read them just fine (the last time I looked, which was many years ago). But my research for this blog post has me thinking that I might not have been seeing the entire picture when I first studied my CD-i samples. I was able to see some of the data, but sources indicate that only proper CD-i hardware is able to see all of the data on the disc (apparently, the TOC doesn’t show all of the sectors on disc).

  Hybrid CDs (Data + Audio)
  At some point, it became a notable selling point for an audio CD to have a data track with bonus features. Even more common (particularly in the early era of CD-ROMs) were computer and console games that used the first track of a disc for all the game code and assets and the remaining tracks for beautifully rendered game audio that could also be enjoyed outside the game. Same model : TOC points to the various tracks and also makes notes about which ones are data and which are audio.

  There seems to be 2 distinct things described above. One type is the mixed mode CD which generally has the data in the first track and the audio in tracks 2..n. Then there is the enhanced CD, which apparently used multisession recording and put the data at the end. I think that the reasoning for this is that most audio CD player hardware would only read tracks from the first session and would have no way to see the data track. This was a positive thing. By contrast, when placing a mixed-mode CD into an audio player, the data track would be rendered as nonsense noise.

  Subchannels
  There’s at least one small detail that my model ignores : subchannels. CDs can encode bits of data in subchannels in sectors. This is used for things like CD-Text and CD-G. I may need to revisit this.

  In Summary
  There’s still a lot of ground to cover, like how those sectors might be formatted to show something useful (e.g., filesystems), and how the model applies to other types of optical discs. Sounds like something for another post.

• How Media Analytics for Piwik gives you the insights you need to measure how effective your video and audio marketing is – Part 1

  31 janvier 2017, par InnoCraft — Community

  Do you have video or audio content on your website or in your app ? If you answered this with yes, you should continue reading and learn everything about our Media Analytics premium feature.

  When you produce video or audio content, you are either spending money or time or often both money and time on your content in the hope of increasing conversions or sales. This means you have to know how your media is being used, when it is used, for how long and by whom. You can simply not afford not to know how this content affects your overall business goals as you are likely losing money and time by not making the most out of it. Would you be able to answer any of the above questions ? Do you know whether you can justify the cost and time for producing them, which videos work better than others and how they support your marketing strategy ? Luckily, getting all these insights is now so trivial it is almost a crime to not measure it.

  Getting Media Analytics and Installation

  Media Analytics can be purchased from the Piwik Marketplace where you find all sorts of free plugins as well as several premium features such as A/B Testing or Funnel. After the purchase you will receive a license key that you can enter in your Piwik to install and update the plugin with just one click.

  The feature will in most cases automatically start tracking your media content and you don’t even need to change the tracking code on your website. Currently supported players are for example YouTube, Vimeo, HTML 5, JW Player, VideoJS and many more players. You can also easily extend it by adding a custom media player or simply by letting us know which player you use and we will add support for it for you.

  By activating this feature, you get more than 15 new media reports, even more exportable widgets, new segments, APIs, and more. We will cover some of those features in this blog post and in part 2. For a full list of features check out the Media Analytics page on the Piwik Marketplace.

  Media Overview

  As the name says, it gives you an overview over your media usage and how it performs over time. You can choose any media metrics in the big evolution graph and the sparklines below give you an overview over all important metrics in a glance.

  

  It lets you for example see how often media was shown to your users, how often users start playing your media, for how long they watched it, how often they finished it, and more. If you see some spikes there, you should definitely have a deeper look at the other reports. When you hover a metric, it will show you a tooltip explaining how the data for this is collected and what it means.

  Real-Time Media

  On the Real-Time page you can see how your content is being used by your visitors right now, for example within the last 30 minutes, last 60 minutes and last 24 hours.

  It shows you how many plays you had in the last minutes, for how long they played it, and it shows you currently most popular media titles. This is great to discover which media content performs best right now and lets you make decisions based on user behaviour that is happening right now.

  

  Below you can see our Audience Real-Time Map that shows you from where in the world your media is being played. A bigger circle indicates that a media play happened more recently and of course you can zoom in down to countries and regions.

  

  All the reports update every few seconds so you can always have a look at it and see in just a second how your content is doing and how certain marketing campaigns affect it. All these real-time reports can be also added as widgets to any of your Piwik Dashboards and they can be exported for example as an iframe.

  Video, Audio and Media Player reports

  Those reports come with so many features, we need a separate blog post and cover this in part 2.

  Events

  Media Analytics will automatically track events so you can see how often users pressed for example play or pause, how often they resumed a video and how often they finished a video. This helps you better understand how your media is being used.

  

  For example in the past we noticed a couple of videos with lots of pause and resume events. We then had a look at the Audience Log – which we will cover next – to better understand why visitors paused the videos so often. We then realized they did this especially for videos that were served from a specific server and because the videos were loading so slow, users often pressed pause to let the media buffer, then played the media for a few seconds and then paused it again as they had to wait for the video to load. Moving those videos to another, faster server showed us immediate results in the number of pauses going down and on average visitors watched the videos for much longer.

  Audience Log

  At InnoCraft, we understand that not only aggregated metrics matter but also that you often need the ability to dig into your data and “debug” certain behaviours to understand the cause for some unusual high or low metrics. For example you may find out that many of your users often pause a video, then you wonder how each individual user behaved so you can better understand the why.

  

  The audience log shows you a detailed log of every visitor. You can chronologically see every action a visitor has performed during their whole visit. If you click on the visitor profile link, you can even see all visits of a specific visitor, and all actions they have ever performed on your website.

  This lets you ultimately debug and understand your visitors and see exactly which actions they performed before playing your media, which media they played, how they played your media, and how they behaved after playing your media.

  The visitor log of course also shows important information about each visitor like where they came from (referrer), their location, software, device and much more information.

  Audience Map

  The Audience Map is similar to the Real-Time Map but it shows you the locations of your visitors based on a selected date range and not in real time. The darker the blue, the more visitors from that country, region or city have interacted with your media.

  

  Coming in part 2

  In the next part we will cover which video, audio and media player reports Media Analytics provides, how segmenting gives you insights into different personas, and how nicely it integrates into Piwik.

  How to get Media Analytics and related features

  You can get Media Analytics on the Piwik Marketplace. If you want to learn more about this feature, you might be also interested in the Media Analytics User Guide and the Media Analytics FAQ.

• How to create a custom theme in Piwik – Introducing the Piwik Platform

  23 août 2014, par Thomas Steur — Development

  This is the start of a new blog series where we introduce the capabilities of the Piwik platform. You’ll learn how to write custom plugins & themes, how to use our HTTP APIs and more.

  We have been greatly simplifying our APIs over the last year focusing primarily on one design principle :

  The complexity of our API should never exceed the complexity of your use case.

  In other words, if you have a simple use for our API, we want it to be simple for you to accomplish it. If you have a complex, big, hairy, change-the-world idea, then maybe we can’t make it simple for you to accomplish it, but we want it to be possible.

  Over the next weeks and months you will learn what exactly we mean by this and how we accomplished it.

  FYI, don’t worry if you’re currently using our APIs, we keep them backwards compatible and we announce breaking changes in our platform changelog.

  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.
  • And if you want, generate some test data : ./console visitorgenerator:generate-visits --idsite=1 --limit-fake-visits=600. This can take a while and requires the VisitorGenerator plugin from the Marketplace.

  Let’s start creating our own theme

  We start by using the Piwik Console to create a blank theme :

  ./console generate:theme

  The command will ask you to enter a name, description and version number for your theme. I will simply use “CustomTheme” as the name of the theme. There should now be a folder plugins/CustomTheme which contains some files to get you started easily.

  Before we modify our theme, we have to activate it by visiting the Settings => Themes admin page in our Piwik installation, or alternatively by running the command ./console core:plugin activate YourCustomTheme. If the theme is not activated, we won’t see any changes.

  Theme Contents

  The most important files in our theme are plugins/CustomTheme/stylesheets/theme.less, plugins/CustomTheme/stylesheets/_colors.less and plugins/CustomTheme/stylesheets/_variables.less :

  • theme.less is the file that will be included when your theme is activated. In this file you would include other stylesheet files and overwrite CSS styles.
  • _colors.less contains many less variables allowing you to easily change the colors Piwik uses.
  • _variables.less contains currently only one variable to change the font family. More variables will be added in the future. Note : This is a new feature and the file will be only there in case you have installed Piwik using Git or at least Piwik 2.6.0.

  Changing the font family

  To change the font family simply overwrite the variable @theme-fontFamily-base: Verdana, sans-serif; in _variables.less. That’s it.

  Changing colors

  To change a color, uncomment the less variables of the colors you want to change in _colors.less. I will shortly explain some of them. Usually changing only these colors will be enough to adjust Piwik’s look to your corporate design or to create a look that pleases you :

  @theme-color-brand:                    #d4291f; // The Piwik red which is for instance used in the menu, it also defines the color of buttons, the little arrows and more
  
  @theme-color-brand-contrast:           #ffffff; // Contrast color to the Piwik red. Usually you need to change it only in case you define a light brand color. For instance to change the text color of buttons
  
  @theme-color-link:                     #1e93d1; // The link color which is usually a light blue
  
  
  
  @theme-color-widget-title-text:        #0d0d0d; // The text and background color of the header of a widget (Dashboard)
  
  @theme-color-widget-title-background:  #f2f2f2;
  
  
  
  @theme-color-menu-contrast-text:       #666666; // The text color of a menu item in the reporting sub menu and the admin menu
  
  @theme-color-menu-contrast-textActive: #0d0d0d; // The text color of an active menu item
  
  @theme-color-menu-contrast-background: #f2f2f2; // The background color of a menu item
  
  
  
  @graph-colors-data-series[1-8]:        #000000; // The different colors used in graphs

  Making the change visible

  To make a color or font change actually visible when you reload a page in Piwik you will have to delete the compiled CSS file after each change like this :

  rm tmp/assets/asset_manager_global_css.css

  Publishing your Theme on the Marketplace

  In case you want to share your theme with other Piwik users you can do this by pushing your theme to GitHub and creating a tag. Easy as that. Read more about how to distribute a theme.

  Advanced features

  Isn’t it easy to create a custom theme ? All we had to do is to change some less variables. We never even created a file ! Of course, based on our API design principle, you can accomplish more if you want. For instance, you can change icons, CSS stylesheets, templates and more.

  For further customising your Piwik, you can even change the logo and favicon in the Settings => General settings page.

  Would you like to know more about theming ? Go to our Theme guide in the Piwik Developer Zone.

  If you have any feedback regarding our APIs or our guides in the Developer Zone feel free to send it to us.

  PS : see also this related FAQ : How do I White Label Piwik ?