RVideo allows you to inspect and process video files.

Installation is a little involved. First, install the gem:

sudo gem install rvideo

Next, install ffmpeg and (possibly) other related libraries. This is documented elsewhere on the web, and can be a headache. If you are on OS X, the Darwinports build is reasonably good (though not perfect). Install with:

sudo port install ffmpeg

Or, for a better build (recommended), add additional video- and audio-related libraries, like this:

sudo port install ffmpeg +lame +libogg +vorbis +faac +faad +xvid +x264 +a52

Most package management systems include a build of ffmpeg, but many include a poor build. So you may need to compile from scratch.

If you want to create Flash Video files, also install flvtool2:

sudo gem install flvtool2

Once ffmpeg and RVideo are installed, you're set.

To inspect a file, initialize an RVideo file inspector object. See the documentation for details.

A few examples:

file = RVideo::Inspector.new(:file => "#{APP_ROOT}/files/input.mp4")

file = RVideo::Inspector.new(:raw_response => @existing_response)

file = RVideo::Inspector.new(:file => "#{APP_ROOT}/files/input.mp4",
                              :ffmpeg_binary => "#{APP_ROOT}/bin/ffmpeg")

file.fps        # "29.97"
file.duration   # "00:05:23.4"

To transcode a video, initialize a Transcoder object.

transcoder = RVideo::Transcoder.new

Then pass a command and valid options to the execute method

recipe = "ffmpeg -i $input_file$ -ar 22050 -ab 64 -f flv -r 29.97 -s"
recipe += " $resolution$ -y $output_file$"
recipe += "\nflvtool2 -U $output_file$"
  transcoder.execute(recipe, {:input_file => "/path/to/input.mp4",
    :output_file => "/path/to/output.flv", :resolution => "640x360"})
rescue TranscoderError => e
  puts "Unable to transcode file: #{e.class} - #{e.message}"

If the job succeeds, you can access the metadata of the input and output files with:

transcoder.original     # RVideo::Inspector object
transcoder.processed    # RVideo::Inspector object

If the transcoding succeeds, the file may still have problems. RVideo will populate an errors array if the duration of the processed video differs from the duration of the original video, or if the processed file is unreadable.

Monitoring ffmpeg encoding progress

Damien Tanner has ported across Jonathan Conway's work on reporting progress on ffmpeg. If you pass a block to your execute it will yield the encoding progress:

transcoder.execute(recipe, {:input_file => "/path/to/input.mp4",
  :output_file => "/path/to/output.flv", :resolution => "640x360"}) do |progress|
  puts "#{progress[:tool].tool_command}: #{progress[:progress]}%"

Progress is only reported for the ffmpeg tool at present, in future hopefully we'll see support extended for more tools.

There is also support for killing hung ffmpeg processes. We found that sometimes a bad file can cause ffmpeg to just stop processing but still sit there using 100% cpu. When monitoring the progress we spawn it off in a separate thread, and then monitor the progress in the main thread. If the ffmpeg process times out by not reporting progress for a specified amount of time, we kill it.

Thanks to Peter Boling for early work on RVideo.

Contribute to RVideo! If you want to help out, there are a few things you can do.

  • Use, test, and submit bugs/patches

  • We need a RVideo::Tools::Mencoder class to add mencoder support.

  • Other tool classes would be great - On2, mp4box, Quicktime (?), etc.

  • Submit other fixes, features, optimizations, and refactorings

If RVideo is useful to you, you may also be interested in RMovie, another Ruby video library. See rmovie.rubyforge.org/ for more.

Finally, watch for Zencoder, a commercial video transcoder built by Slantwise Design. Zencoder uses RVideo for its video processing, but adds file queuing,

distributed transcoding, a web-based transcoder dashboard, and more. See zencoder.tv or slantwisedesign.com for more.

Copyright © 2007 Jonathan Dahl and Slantwise Design. Released under the MIT license.