2595f18b2f
Fix certain animated PNGs returning NaN as the duration because the frame rate was being reported as "0/0" by FFMpeg. This happens when the animation has zero delay between frames. This is supposed to mean a PNG with an infinitely fast frame rate, but in practice browsers limit it to around 10FPS. The exact frame rate browsers will use is unknown and implementation defined.
97 lines
2.4 KiB
Ruby
97 lines
2.4 KiB
Ruby
require "shellwords"
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# A wrapper for the ffmpeg command.
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class FFmpeg
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extend Memoist
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class Error < StandardError; end
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attr_reader :file
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# Operate on a file with FFmpeg.
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# @param file [File, String] a webm, mp4, gif, or apng file
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def initialize(file)
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@file = file.is_a?(String) ? File.open(file) : file
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end
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# Generate a .png preview image for a video or animation. Generates
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# thumbnails intelligently by avoiding blank frames.
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#
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# @return [MediaFile] the preview image
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def smart_video_preview
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vp = Tempfile.new(["video-preview", ".png"], binmode: true)
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# https://ffmpeg.org/ffmpeg.html#Main-options
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# https://ffmpeg.org/ffmpeg-filters.html#thumbnail
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output = shell!("ffmpeg -i #{file.path.shellescape} -vf thumbnail=300 -frames:v 1 -y #{vp.path.shellescape}")
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Rails.logger.debug(output)
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MediaFile.open(vp)
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end
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# Get file metadata using ffprobe.
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# @see https://ffmpeg.org/ffprobe.html
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# @see https://gist.github.com/nrk/2286511
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# @return [Hash] a hash of the file's metadata
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def metadata
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output = shell!("ffprobe -v quiet -print_format json -show_format -show_streams #{file.path.shellescape}")
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json = JSON.parse(output)
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json.with_indifferent_access
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end
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def width
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video_streams.first[:width]
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end
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def height
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video_streams.first[:height]
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end
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def duration
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metadata.dig(:format, :duration).to_f
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end
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def frame_count
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if video_streams.first.has_key?(:nb_frames)
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video_streams.first[:nb_frames].to_i
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else
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(duration * frame_rate).to_i
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end
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end
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# @return [Float, nil] The frame rate of the video or animation, or nil if
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# unknown. The frame rate can be unknown for animated PNGs that have zero
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# delay between frames.
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def frame_rate
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rate = video_streams.first[:avg_frame_rate] # "100/57"
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numerator, denominator = rate.split("/")
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if numerator.to_f == 0 || denominator.to_f == 0
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nil
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else
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(numerator.to_f / denominator.to_f)
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end
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end
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def video_streams
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metadata[:streams].select { |stream| stream[:codec_type] == "video" }
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end
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def audio_streams
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metadata[:streams].select { |stream| stream[:codec_type] == "audio" }
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end
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def has_audio?
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audio_streams.present?
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end
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def shell!(command)
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program = command.shellsplit.first
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output, status = Open3.capture2e(command)
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raise Error, "#{program} failed: #{output}" if !status.success?
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output
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end
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memoize :metadata
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end
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