Movie problems in LiveCode

[Richard Gaskin]

stgoldberg wrote:

 >>On 3/24/2015 10:26 AM, Richard Gaskin wrote:
 >
 >> I've always been wary of shipping things that rely on
 >>relative paths, since any other script can change the
 >>default directory out from under me at any time.
 >>In apps where the media I'm playing resides in a single
 >>folder. I often just have a central handler cover that to
 >>which I pass the file's short name only and it takes care
 >>of the rest, e.g.:
 >>
 >> on PlayMovie pFile
 >>    put specialFolderPath("documents")&"/MyApp/media/"& pFile into
 > tPath
 >>    if there is not a file tPath then
 >>       answer "Media file missing: "& tPath
 >>       exit to top
 >>    end if
 >>    play tPath
 >> end PlayMovie
 >
 >>Jackie Landman Gay wrote:
 >>That's exactly what I do too, I've never trusted relative paths.
 >
 > Richard and Jackie, does your reluctance to use relative paths
 > also extend to the distribution of standalones, or is it just stacks
 > that present the problem?

It's not so much a problem (at least not while QuickTime existed) as it 
is an opportunity to centralize program logic for easier scripting in 
the short term and easier maintenance over the long term.

Without centralizing the playback handling, I'd need to write paths to 
the media and check for the file's existence everywhere throughout my 
code that I need to play a movie.

By centralizing it in a common handler, the scripts that call it are 
very short:

   on mouseUp
       PlayMovie "SomeFile.mov"
   end mouseUp

...and all the details for how that file is found, verified to exist, 
and then played are handled in one handler.

So there's an immediate benefit while I'm writing the program, and it 
only gets better over time:  if I later need to change anything about 
how movies are played, I change only one handler and everything 
throughout my app that calls it benefits from that change immediately 
without any of those calls needing to be changed themselves.


 > I’m not experienced enough to follow the above script.
 > Perhaps you can recommend a place where I can find a more
 > detailed explanation.

The Dictionary entry for the specialFolderPath function is good reading, 
and worth taking some time to experiment with.

For security reasons, OSes are increasingly limiting the places 
applications can access files.  The specialFolderPath function returns 
the path to a good many "special" folders, directories the OS guidelines 
recommend for certain types of files, such as Preferences and 
Application Support, and handles constants for other commonly-used 
folders like Desktop and Home.

All that's happening in that handler is using that function to build a 
full path at runtime, with an additional step to make sure the file 
exists (you never know what people might do with stuff after it's 
installed, which is why more than 30% of an app's code on average isn't 
feature-related but merely error-checking).

Let's look at each part:

   put specialFolderPath("documents")&"/MyApp/media/"& pFile into tPath

This calls the specialFolderPath function, asking for the path to the 
Documents folder.  Mac, Windows, and Linux all have a Documents folder, 
the recommended place for users to store files they create with your app.

For files your app creates or installs itself it may be better to use 
another folder to install those into, but the recommended location is a 
bit different for each OS.  I can provide a handler for that if needed, 
but for now we'll keep things simple here using one of the special 
folders consistently supported across OSes.


This second bit just ensures the file exists, informing the user if it's 
been removed:

   if there is not a file tPath then
      answer "Media file missing: "& tPath
      exit to top
   end if

The last line just plays the file:

   play tPath

If somewhere down the road is became necessary for the engine team to 
change the play command to something like "PlayVideo", with this 
centralized handler you just make that change in one place and 
everything in your app immediately benefits without any other changes.

If you if need to add more error-checking, or handle platform-specific 
considerations, or just about anything else, without a centralized 
handler you'd need to replicate that code throughout your app every time 
you want to play a movie.

Much simpler to just write:

    PlayMovie "SomeMovie.mov"

...and let one script to all the work for you in one place.

-- 
  Richard Gaskin
  Fourth World Systems
  Software Design and Development for the Desktop, Mobile, and the Web
  ____________________________________________________________________
  Ambassador at FourthWorld.com                http://www.FourthWorld.com