Streamio FFMPEG

Simple yet powerful wrapper around the ffmpeg command for reading metadata and transcoding movies.

All work on this project is sponsored by the online video platform Streamio.



(sudo) gem install streamio-ffmpeg



Only guaranteed to work with MRI Ruby 1.9.3 or later. Should work with rubinius head in 1.9 mode. Will not work in jruby until they fix: (should work in the upcoming 1.7.5)


The current gem is tested against ffmpeg 1.2.1. So no guarantees with earlier (or much later) versions. Output and input standards have inconveniently changed rather a lot between versions of ffmpeg. My goal is to keep this library in sync with new versions of ffmpeg as they come along.


Require the gem

require 'rubygems'
require 'streamio-ffmpeg'

Reading Metadata

movie ="path/to/")

movie.duration # 7.5 (duration of the movie in seconds)
movie.bitrate # 481 (bitrate in kb/s)
movie.size # 455546 (filesize in bytes)

movie.video_stream # "h264, yuv420p, 640x480 [PAR 1:1 DAR 4:3], 371 kb/s, 16.75 fps, 15 tbr, 600 tbn, 1200 tbc" (raw video stream info)
movie.video_codec # "h264"
movie.colorspace # "yuv420p"
movie.resolution # "640x480"
movie.width # 640 (width of the movie in pixels)
movie.height # 480 (height of the movie in pixels)
movie.frame_rate # 16.72 (frames per second)

movie.audio_stream # "aac, 44100 Hz, stereo, s16, 75 kb/s" (raw audio stream info)
movie.audio_codec # "aac"
movie.audio_sample_rate # 44100
movie.audio_channels # 2

movie.valid? # true (would be false if ffmpeg fails to read the movie)


First argument is the output file path.

movie.transcode("tmp/movie.mp4") # Default ffmpeg settings for mp4 format

Keep track of progress with an optional block.

movie.transcode("movie.mp4") { |progress| puts progress } # 0.2 ... 0.5 ... 1.0

Give custom command line options with a string.

movie.transcode("movie.mp4", "-ac aac -vc libx264 -ac 2 ...")

Use the EncodingOptions parser for humanly readable transcoding options. Below you'll find most of the supported options. Note that the :custom key will be used as is without modification so use it for any tricky business you might need.

options = {video_codec: "libx264", frame_rate: 10, resolution: "320x240", video_bitrate: 300, video_bitrate_tolerance: 100,
           aspect: 1.333333, keyframe_interval: 90,
           x264_profile: "high", x264_preset: "slow",
           audio_codec: "libfaac", audio_bitrate: 32, audio_sample_rate: 22050, audio_channels: 1,
           threads: 2,
           custom: "-vf crop=60:60:10:10"}
movie.transcode("movie.mp4", options)

The transcode function returns a Movie object for the encoded file.

transcoded_movie = movie.transcode("tmp/movie.flv")

transcoded_movie.video_codec # "flv"
transcoded_movie.audio_codec # "mp3"

Aspect ratio is added to encoding options automatically if none is specified.

options = { resolution: "320x180" } # Will add -aspect 1.77777777777778 to ffmpeg

Preserve aspect ratio on width or height by using the preserve_aspect_ratio transcoder option.

widescreen_movie ="path/to/")

options = { resolution: "320x240" }

transcoder_options = { preserve_aspect_ratio: :width }
widescreen_movie.transcode("movie.mp4", options, transcoder_options) # Output resolution will be 320x180

transcoder_options = { preserve_aspect_ratio: :height }
widescreen_movie.transcode("movie.mp4", options, transcoder_options) # Output resolution will be 426x240

For constant bitrate encoding use video_min_bitrate and video_max_bitrate with buffer_size.

options = {video_min_bitrate: 600, video_max_bitrate: 600, buffer_size: 2000}
movie.transcode("movie.flv", options)

Taking Screenshots

You can use the screenshot method to make taking screenshots a bit simpler.


The screenshot method has the very same API as transcode so the same options will work.

movie.screenshot("screenshot.bmp", seek_time: 5, resolution: '320x240')

You can preserve aspect ratio the same way as when using transcode.

movie.screenshot("screenshot.png", { seek_time: 2, resolution: '200x120' }, preserve_aspect_ratio: :width)

Specify the path to ffmpeg

By default, streamio assumes that the ffmpeg binary is available in the execution path and named ffmpeg and so will run commands that look something like "ffmpeg -i /path/to/input.file ...". Use the FFMPEG.ffmpeg_binary setter to specify the full path to the binary if necessary:

FFMPEG.ffmpeg_binary = '/usr/local/bin/ffmpeg'

This will cause the same command to run as "/usr/local/bin/ffmpeg -i /path/to/input.file ..." instead.

Automatically kill hung processes

By default, streamio will wait for 30 seconds between IO feedback from the FFMPEG process. After which an error is logged and the process killed. It is possible to modify this behaviour by setting a new default:

# Change the timeout
Transcoder.timeout = 10

# Disable the timeout altogether
Transcoder.timeout = false

Disabling output file validation

By default Transcoder validates the output file, in case you use FFMPEG for HLS format that creates multiple outputs you can disable the validation by passing validate: false to transcoder_options.

Note that transcode will not return the encoded movie object in this case since attempting to open a (possibly) invalid output file might result in an error being raised.

transcoder_options = { validate: false }
movie.transcode("movie.mp4", options, transcoder_options) # returns nil


Copyright (c) Streamio AB. See LICENSE for details.