ffmpeg-ruby

Summary

ffmpeg-ruby is a ruby C extension binding to ffmpeg/libav* library.

It's main purpose (at least for now) is to extract frame in order to make video thumbnails. It also give access to main video attributes (frame rate, bit rate, duration, codecs, ...)

Installation

ffmpeg-ruby requires a patched version of ffmpeg. This is due to a conflict between ruby and ffmpeg macros. Warning: If you do not patch it, all conversion between C numbers to Ruby won't be accurate (0 = 1 :( )

Download latest sources of ffmpeg :

wget http://ffmpeg.mplayerhq.hu/ffmpeg-export-snapshot.tar.bz2
tar xjvf ffmpeg-export-snapshot.tar.bz2
cd ffmpeg-export-20*

Patch it to rename RSHIFT macro :

for file in `grep -ril RSHIFT .`; do ruby -i.bak -pe "gsub(/RSHIFT/, 'FFM_RSHIFT')" $file; done

If your on Mac OS X as I do, you need to patch libswale too :

ruby -i.bak -pe 'gsub(%r|defined\(ARCH_X86\) && defined\(CONFIG_GPL\)|, %q{defined(ARCH_X86) && defined(CONFIG_GPL) && !defined(__APPLE__)})' libswscale/rgb2rgb.c

Configure with some prefix :

--enable-swscale is mandatory, feel free to add some configuration options

./configure --prefix=/opt/ffmpeg --enable-pthreads --enable-shared --enable-gpl --enable-swscale
make
sudo make install

You can now continue with ffmpeg-ruby.

git checkout git://github.com/gwik/ffmpeg-ruby.git

cd ffmpeg-ruby
gem build ./ffmpeg-ruby.gemspec
sudo gem install ./ffmpeg-ruby-0.1.0.gem -- --with-ffmpeg-dir=/opt/ffmpeg

You can now test it :

irb
>> require 'rubygems'
=> false
>> require 'ffmpeg'
=> true
>> FFMPEG
=> FFMPEG

Tutorial

ffmpeg-ruby does not have real document YET (I promise it will change soom). You can take a look a specs for in depth usage.

Here is basic usage.

Video attributes

require 'rubygems'
require 'ffmpeg'

video = FFMPEG::InputFormat.new('alligator.mp4')
=> #<FFMPEG::InputFormat:0x5fa3c0>

video.public_methods - Object.public_instance_methods
=> ["bit_rate", "filename", "duration", "has_stream_with_codec_type?", "first_video_stream", "human_duration", "has_video?", "video_stream_count", "streams", "has_audio?", "first_audio_stream", "audio_stream_count"]

Streams

>> video.first_video_stream.public_methods - Object.public_instance_methods
=> ["position", "duration", "index", "codec", "decode_frame", "seek"]

Seeking in stream

video.first_video_stream.seek(10)
video.first_video_stream.position
=> 10.2333333333333

As you can see, seeking is not very precise.

Extracting frame

frame = video.first_video_stream.decode_frame
=> #<FFMPEG::Frame:0x5c9874>

"frame size #{frame.width}x#{frame.height}"
=> "frame size 240x176"

Animated GIF example with RMagick

See animated_gif_example.rb