Rails - Sep 2007 - How do i make rails wait until an ffmpeg call is complete?

In my app i upload a file, convert it with ffmpeg, delete the original
and make a small thumbnail out of the big thumbnail ffmpeg makes.

At the moment it seems like these actions are tripping over each other -
how can i make the app wait until ffmpeg has completed it''s output
before doing the next thing?
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On 18 Sep 2007, at 18:56, Max Williams wrote:
> In my app i upload a file, convert it with ffmpeg, delete the original
> and make a small thumbnail out of the big thumbnail ffmpeg makes.
>
> At the moment it seems like these actions are tripping over each  
> other -
> how can i make the app wait until ffmpeg has completed it''s output
> before doing the next thing?
Why don''t you consider the following setup:
- Let the user upload the movie
- Hand the movie over to Backgroundrb for processing and render a  
"Movie being processed"-message and a PeriodicalUpdater to your view
- In the PeriodicalUpdater method, query Backgroundrb to see if the  
processing is finished
- If it''s finished, render it in the page

This way, you''ll avoid locking up one of your mongrels during a  
possible long running process (and movie processing tends to be a  
long running process). On top of that, the user can continue working  
with your application while the processing is taking place. It might  
require you to rethink your interface a bit, but the user experience  
will be substantially improved.

Best regards

Peter De Berdt


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Peter De Berdt wrote:
> On 18 Sep 2007, at 18:56, Max Williams wrote:
> 
> Why don''t you consider the following setup:
> - Let the user upload the movie
> - Hand the movie over to Backgroundrb for processing and render a
> "Movie being processed"-message and a PeriodicalUpdater to your
view
> - In the PeriodicalUpdater method, query Backgroundrb to see if the
> processing is finished
> - If it''s finished, render it in the page
> 
> 
> Best regards
> 
> Peter De Berdt
That sounds like it might be a nice idea, but i don''t really have time
to do anything as nice as that at the moment - i just need a simple way
to make the program wait...
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Could you post your code, as far as I know, the ´ffmpeg xxxxx´calls  
from ruby execute synchronically, so it should wait before going  
further.

On 18 Sep 2007, at 19:32, Max Williams wrote:
> That sounds like it might be a nice idea, but i don''t really have
time
> to do anything as nice as that at the moment - i just need a simple  
> way
> to make the program wait...


Best regards

Peter De Berdt


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Peter De Berdt wrote:
> Could you post your code, as far as I know, the ´ffmpeg xxxxx´calls
> from ruby execute synchronically, so it should wait before going
> further.
> 
> On 18 Sep 2007, at 19:32, Max Williams wrote:
> 
>> That sounds like it might be a nice idea, but i don''t really
have time
>> to do anything as nice as that at the moment - i just need a simple  
>> way
>> to make the program wait...
> 
> 
> 
> Best regards
> 
> Peter De Berdt
Funny you should say that, i just discovered i was passing an option 
that told it to only do the first second!

Basically i am an idiot...

Thanks for your advice!
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I''d be interested in seeing your code. Is it available?

On Sep 18, 9:56 am, Max Williams
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> In my app i upload a file, convert it with ffmpeg, delete the original
> and make a small thumbnail out of the big thumbnail ffmpeg makes.
>
> At the moment it seems like these actions are tripping over each other -
> how can i make the app wait until ffmpeg has completed it''s output
> before doing the next thing?
> --
> Posted viahttp://www.ruby-forum.com/.

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eggie5 wrote:
> I''d be interested in seeing your code. Is it available?
> 
> On Sep 18, 9:56 am, Max Williams
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
Sure - here''s my method, i''m *currently* passing it this value
for
''command'', generated from some other methods.  Previously i
had "-t 001"
as well which was the real reason my movies were truncated - that says 
"only do the first second":  with that dodgy option removed, it works 
fine.  I''d still be interested in advice for taking the standard output
progress report in the method and using it to inform the user of 
progress, though.  And how to tell the user about uploading progress? 
(uploading is slower than the conversion)

 #{RAILS_ROOT}/public/ffmpeg/ffmpeg
 -i 
#{RAILS_ROOT}/public/data/unconverted_movies/temp#{self.id}.#{self.filetype}
 -ar 22050 #{RAILS_ROOT}/public/data/movies/mov#{self.id}.flv
 -f mjpeg 
#{RAILS_ROOT}/public/data/movies/mov_thumbs/mov_thumb#{self.id}.jpeg

  ##################################################################
  #method: execute_ffmpeg
  #This method provides some exception tracking and also progress
  #tracking for file conversion with ffmpeg.
  #TODO:  Work out how to use the progress text it puts into
  #standard output to show progress to the user.
  #
  #NOTE - this method is taken from the blog of Dmytro Shteflyuk:
  #http://kpumuk.info/ruby-on-rails/encoding-media-files-in-ruby-
  #using-ffmpeg-mencoder-with-progress-tracking/
  #params:
  #
  ##################################################################
  def execute_ffmpeg(command)
    progress = nil
    IO.popen(command) do |pipe|
      pipe.each("\r") do |line|
        if line =~ /Duration: (\d{2}):(\d{2}):(\d{2}).(\d{1})/
          duration = (($1.to_i * 60 + $2.to_i) * 60 + $3.to_i) * 10 + 
$4.to_i
        end
        if line =~ /time=(\d+).(\d+)/
          if not duration.nil? and duration != 0
            p = ($1.to_i * 10 + $2.to_i) * 100 / duration
          else
            p = 0
          end
          p = 100 if p > 100
          if progress != p
            progress = p
            print "PROGRESS: #{progress}\n"
            $defout.flush
          end #if progress
        end #if line =~
      end#pipe.each
    end#IO.popen
    raise MediaFormatException if $?.exitstatus != 0
  end#method
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On 19 Sep 2007, at 10:24, Max Williams wrote:
> Sure - here''s my method, i''m *currently* passing it this
value for
> ''command'', generated from some other methods.  Previously
i had "-t
> 001"
> as well which was the real reason my movies were truncated - that says
> "only do the first second":  with that dodgy option removed, it
works
> fine.  I''d still be interested in advice for taking the standard  
> output
> progress report in the method and using it to inform the user of
> progress, though.  And how to tell the user about uploading progress?
> (uploading is slower than the conversion)
Upload progress: use one of the many "ajax upload solutions" out  
there. I really like SWFUpload, because it''s the Flash file that  
streams the upload to the server that keeps track of the upload  
progress. Other solutions mostly rely on serverside tracking.

For the progress report on the conversion, your method makes it  
impossible, because Rails can only return information at the end of  
the request and your method only completes after the conversion. The  
only way to accomplish what you''re looking for, is passing the rails  
request on to backgroundrb, and use a PeriodicalUpdater (or some push  
technology, but that''s even more complex) to query the backgroundrb  
worker.


Best regards

Peter De Berdt


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Peter De Berdt wrote:
> On 19 Sep 2007, at 10:24, Max Williams wrote:
> 
> Upload progress: use one of the many "ajax upload solutions" out
> there. I really like SWFUpload, because it''s the Flash file that
> streams the upload to the server that keeps track of the upload
> progress. Other solutions mostly rely on serverside tracking.
> 
> For the progress report on the conversion, your method makes it
> impossible, because Rails can only return information at the end of
> the request and your method only completes after the conversion. The
> only way to accomplish what you''re looking for, is passing the
rails
> request on to backgroundrb, and use a PeriodicalUpdater (or some push
> technology, but that''s even more complex) to query the
backgroundrb
> worker.
> 
> 
> Best regards
> 
> Peter De Berdt
Thanks for the uploading tip!  As far as conversion goes though, the 
method i''m using is writing progress info to standard output, there
must
be a simple way of displaying this in a dynamic view?  Would i need ajax 
again?  (i''ve not used ajax at all)

cheers
max
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On 19 Sep 2007, at 16:34, Max Williams wrote:
> Thanks for the uploading tip!  As far as conversion goes though, the
> method i''m using is writing progress info to standard output,
there
> must
> be a simple way of displaying this in a dynamic view?  Would i need  
> ajax
> again?  (i''ve not used ajax at all)
If you just want to capture the output of the command once it''s  
finished and not while it''s working on a file (haven''t used
ffmpeg
yet so you''ll have to look into the output yourself), you can just  
use something like

result = ´ls -l /usr/bin/´

If you want progress (each percentage prints out a new line in the  
terminal), you''re best off using backgroundrb to handle the process.

A rails request has the following lifecycle:
* User enters a url
* Url is routed to the controller method
* Controller method executes step by step, so if you use a ´command´  
it''s one of those steps that needs to execute before going to the  
next line of code
* View is rendered

There''s a good introductory blog post at http://www.infoq.com/ 
articles/BackgrounDRb


Best regards

Peter De Berdt


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Peter De Berdt wrote:
> On 19 Sep 2007, at 16:34, Max Williams wrote:
> 
> There''s a good introductory blog post at http://www.infoq.com/
> articles/BackgrounDRb
> 
> 
> Best regards
> 
> Peter De Berdt
Cool, thanks for all your help.

max
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