Paperclip thumbnail generation uses magic?

Rails
1

I have been using CarrierWave for file uploads on a site which needs to
accept a really wide range of different movie formats, stills, PDFs…
And I have been struggling with making thumbnails of certain formats.
After much yak-shaving with ffmpeg and imagemagick and Rmagick, I
finally decided to do a little spike app with nothing but Paperclip. I
set up the simplest thing that could possibly work:

has_attached_file :blob, :styles => { :thumb => [“320x320>”, :png],
:large => [“1500x1500>”, :png] }

And no matter what format (within reason) I pass to it, I get a nicely
formed PNG format thumbnail and large preview image. PSD, PDF, TIFF,
MOV, M4V – it Just Works. And I cannot figure out how it is doing this,
despite reading through the source code for quite a while.

The reason why I need to access the magic is that while I am getting a
nice thumbnail from any movie format I pass in, I am getting the very
first frame of the movie (usually black) rather than a few seconds into
the clip. In my CarrierWave converter, I had a custom offset time
defined for this. But I cannot see where Paperclip is defining what to
do with a video to generate a PNG image so I can alter this default.

There are tons of examples on SO and the Web in general, showing how to
create a custom video thumbnailer and transcoder, but I would like to
avoid rebuilding this wheel that Paperclip seems to have hewn out of
pure Elven magick.

Thanks in advance,

Walter

2

I haven’t seen the paperclip code but I think you can look at the
preprocessors used by default by paperclip.
You usually see logs when paperclip does some processing using rmagick
which may be a clue as to what
part of the lib you want to look at.

On Wed, Jun 12, 2013 at 11:15 PM, Walter Lee D.
[email protected]wrote:

And no matter what format (within reason) I pass to it, I get a nicely

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3

Thanks, that’s good advice. The console told the tale. It appears as
though ImageMagick is delegating to ffmpeg, and the convert function
that Paperclip generates in their thumbnail operation tacks a [0] to the
end of the filename to get it to use the first frame. I need to do some
more digging, but it appears as though I can just put a different number
in there for movies. It seems as though all file types are getting the
[0] treatment, not just movies, so I don’t want to start looking for
frame 10 in a TIFF…

Walter

4

you may want to put this into something that loads when you app loads,
like initializers/paperclip.rb

Paperclip.options[:log] = true