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• What is “interoperable TTML” ?

  1er janvier 2014, par silvia

  I’ve just tried to come to terms with the latest state of TTML, the Timed Text Markup Language.

  TTML has been specified by the W3C Timed Text Working Group and released as a RECommendation v1.0 in November 2010. Since then, several organisations have tried to adopt it as their caption file format. This includes the SMPTE, the EBU (European Broadcasting Union), and Microsoft.

  Both, Microsoft and the EBU actually looked at TTML in detail and decided that in order to make it usable for their use cases, a restriction of its functionalities is needed.

  EBU-TT

  The EBU released EBU-TT, which restricts the set of valid attributes and feature. “The EBU-TT format is intended to constrain the features provided by TTML, especially to make EBU-TT more suitable for the use with broadcast video and web video applications.” (see EBU-TT).

  In addition, EBU-specific namespaces were introduce to extend TTML with EBU-specific data types, e.g. ebuttdt:frameRateMultiplierType or ebuttdt:smpteTimingType. Similarly, a bunch of metadata elements were introduced, e.g. ebuttm:documentMetadata, ebuttm:documentEbuttVersion, or ebuttm:documentIdentifier.

  The use of namespaces as an extensibility mechanism will ascertain that EBU-TT files continue to be valid TTML files. However, any vanilla TTML parser will not know what to do with these custom extensions and will drop them on the floor.

  Simple Delivery Profile

  With the intention to make TTML ready for “internet delivery of Captions originated in the United States”, Microsoft proposed a “Simple Delivery Profile for Closed Captions (US)” (see Simple Profile). The Simple Profile is also a restriction of TTML.

  Unfortunately, the Microsoft profile is not the same as the EBU-TT profile : for example, it contains the “set” element, which is not conformant in EBU-TT. Similarly, the supported style features are different, e.g. Simple Profile supports “display-region”, while EBU-TT does not. On the other hand, EBU-TT supports monospace, sans-serif and serif fonts, while the Simple profile does not.

  Thus files created for the Simple Delivery Profile will not work on players that expect EBU-TT and the reverse.

  Fortunately, the Simple Delivery Profile does not introduce any new namespaces and new features, so at least it is an explicit subpart of TTML and not both a restriction and extension like EBU-TT.

  SMPTE-TT

  SMPTE also created a version of the TTML standard called SMPTE-TT. SMPTE did not decide on a subset of TTML for their purposes – it was simply adopted as a complete set. “This Standard provides a framework for timed text to be supported for content delivered via broadband means,…” (see SMPTE-TT).

  However, SMPTE extended TTML in SMPTE-TT with an ability to store a binary blob with captions in another format. This allows using SMPTE-TT as a transport format for any caption format and is deemed to help with “backwards compatibility”.

  Now, instead of specifying a profile, SMPTE decided to define how to convert CEA-608 captions to SMPTE-TT. Even if it’s not called a “profile”, that’s actually what it is. It even has its own namespace : “m608 :”.

  Conclusion

  With all these different versions of TTML, I ask myself what a video player that claims support for TTML will do to get something working. The only chance it has is to implement all the extensions defined in all the different profiles. I pity the player that has to deal with a SMPTE-TT file that has a binary blob in it and is expected to be able to decode this.

  Now, what is a caption author supposed to do when creating TTML ? They obviously cannot expect all players to be able to play back all TTML versions. Should they create different files depending on what platform they are targeting, i.e. a EBU-TT version, a SMPTE-TT version, a vanilla TTML version, and a Simple Delivery Profile version ? Should they by throwing all the features of all the versions into one TTML file and hope that the players will pick out the right things that they require and drop the rest on the floor ?

  Maybe the best way to progress would be to make a list of the “safe” features : those features that every TTML profile supports. That may be the best way to get an “interoperable TTML” file. Here’s me hoping that this minimal set of features doesn’t just end up being the usual (starttime, endtime, text) triple.

  UPDATE :

  I just found out that UltraViolet have their own profile of SMPTE-TT called CFF-TT (see UltraViolet FAQ and spec). They are making some SMPTE-TT fields optional, but introduce a new @forcedDisplayMode attribute under their own namespace “cff :”.

• Piwik now integrated within CloudFlare

  8 novembre 2017, par Piwik Core Team — Development

  Would you like to know some quick fix in order to make your website load faster ? Would you like your users to have a better experience on your website ? One answer to that is what we call a CDN. Content Delivery Network (CDN) is a system of distributed servers that deliver content to a user based on various criterias such as geolocation.

  And the good news for you is that Piwik got recently integrated to a popular CDN : CloudFlare.

  What is CloudFlare ?

  As previously said, CloudFlare is a content delivery network (CDN).

  

  The three major advantages of using CloudFlare as a CDN are :

  • it is making your website load faster by providing a nearby location to your files to users
  • it also help detecting potential attacks like DDoS and takes away these risks for you
  • it runs one of the largest, fastest, and most reliable managed DNS service in the world

  Automatically add Piwik tracking code to your website

  With the integration of Piwik to CloudFlare, you can now deploy the Piwik tracking code directly through your CloudFlare account instead of tweaking the source code of your website.

  In order to do that, all you need is to log in to your CloudFlare account and click on “Apps”. Then look for Piwik within the search bar :

  

  Once done, click on “Preview” on your site to enter your credentials (Piwik URL and website ID) :

  

  Click “install” to finish the setup. The Piwik tracking code is now installed on each page of your website.

  If you have previously added the tracking code manually to your website and now use the Piwik app, don’t forget to remove the tracking code from your website. Otherwise you end up tracking every user twice.

  Important note : the Piwik CloudFlare integration only concerns the Piwik tracking code integration. For the Piwik app on Cloudflare to work you will need to have a running Piwik installed on your server, or you can start a free trial on the Piwik Analytics Cloud.

  To learn more about what Piwik integration to CloudFlare can do for you.

• How to delay subtitles in ffmpeg ? [closed]

  31 juillet 2022, par friendlygiraffe

  Using ffmpeg, I am burning subtitles to a movie using the following :

  



  ffmpeg -i inputfile.mov -vf "subtitles=subtitles.srt:force_style='Alignment=9,Fontsize=8,Outline=0'" $outputfile.mov


  



  Is there a way of delaying/shifting the subtitles start point ? 
Eg have all the subs start 2 seconds later ?