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DAY 26
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Ruby on Rails 與它們相關的東西系列 第 26

Day26 - Ruby on Rails 中使用 FFmpeg 處理影音轉檔、合併、上字幕

前言

FFmpeg 是一個開放原始碼的自由軟體,可以執行音訊和視訊多種格式的錄影、轉檔、串流功能,包含了libavcodec——這是一個用於多個專案中音訊和視訊的解碼器函式庫,以及libavformat——一個音訊與視訊格式轉換函式庫。 「FFmpeg」這個單詞中的「FF」指的是「Fast Forward」。

以上擷取自 Wiki 介紹

前陣子在處理影片時,以 Ruby on Rails 實作,將多個影片合併、剪輯指定時間範圍 (ex: 影片長度 00:30 ,只保留 00:05 ~ 00:15 的畫面)、上字幕、合併成一個檔案,透過 FFmpeg 來處理

後續的文章會以此 repo 作為範例

備註: 本文以此影片為例 Digital Countdown Timer (出處: Videvo)

如何安裝

雖然在 RubyGems 中搜尋「FFmpeg」能找到一些 Gem 使用,但這次不透過 Gem ,直接在 MacOS / Linux 環境直接安裝 FFmpeg 使用,在終端機輸入

備註: 此文以 ffmpeg version 4.3.1 版本為範例

# MacOS、Linux 原生不支援這指令

# MacOS 安裝指令
brew install ffmpeg

# note: 安裝完成後,輸入 ffmpeg -v 確認版本及是否安裝成功

如何轉檔

終端機輸入

ffmpeg -i input_video.mkv -codec copy output_video.mp4

# 範例:
ffmpeg -i DigitalCountdownTimerVidevo.mov -codec copy test.mp4

如何合併

例如想把多支影片合併,將 Milky Way TimelapseDigital Countdown Timer 合併,可用以下方法,或參考 Stack Overflow 這篇

# 檔案名稱不要有空格 (檔案路徑要是正確的喔)
# list.txt
file Saint_Barthelemy.mov
file DigitalCountdownTimerVidevo.mov

# ---

ffmpeg -f concat -i list.txt -c copy output.mp4

如何剪輯指定時間範圍

需特別留意計算方式是從 mm:ss (格式為 00:04 ,4 碼) 開始,接著計算保留的「長度」,不是直接寫該影片想結束的位置喔

ffmpeg -ss mm:ss -to mm2:ss2 -i video.mp4 -codec copy output.mp4

# 範例
# 從該影片 00:03 秒開始,保留長度為 5 秒 (至該影片 00:08 秒位置,不能直接寫 00:08 喔)
ffmpeg -ss 00:03 -t 00:05 -i DigitalCountdownTimerVidevo.mov output.mp4

如何上字幕

字幕格式有多種,常見有 SRT、SSA、ASS、SUB、TTS、WebVTT...等,單純上字幕不加任何效果,可用 SRT,若想要調整字形、字體大小、顏色、位置...等比較進階處理的話,可考慮直接用 ASS

備註: 以 ffmpeg version 4.3.1 為例,原生不支援 WebVTT

# srt.srt
1
00:00:00,000 --> 00:00:05,000
Hello World
2
00:00:05,000 --> 00:00:10,000
看得到

# ---

# 將字幕嵌入影片中
ffmpeg -i DigitalCountdownTimerVidevo.mov -vf 'subtitles=srt.srt' output.mp4

# 指定字幕大小
ffmpeg -i DigitalCountdownTimerVidevo.mov -vf "subtitles=srt.srt:force_style='Fontsize=32'" output.mp4

# 備註: 針對字幕要做比較多處理的話,建議直接用 ASS 先調好,再嵌入比較方便

如何限制 CPU 使用量 (非必要)

Linux 文章系列,有提到 nice 與 cpulimit 指令,若想限制 CPU 使用量的話,可結合使用

# 說明: CPU 上限為 30% ,且使用雙核心處理 (threads 2)
nice -n 20 cpulimit -l 30 ffmpeg -threads 2 -i DigitalCountdownTimerVidevo.mov output.mp4

實際轉檔過程,htop 畫面

實作範例

上面都是在終端機操作,以下示範在 Sidekiq 上使用 FFmpeg 處理,可參考此 commit

備註:

  1. 該範例為先下載影片、並限制 CPU 使用量在 80%
  2. 若想測試,可在 rails console 輸入 Video::HandleVideoWorker.new.perform 或先 cd Video::HandleVideoWorker.new 再接著輸入 perform
# config/sidekiq.yml
- ['video_worker', 10]



# app/worker/video/handle_video_worker.rb
module Video
  class HandleVideoWorker
    include Sidekiq::Worker
    sidekiq_options retry: 0, dead: true, queue: 'video_worker'

    VIDEO_PATH = Rails.root.join('data/attachments/videos')

    # NOTE:
    # need install ffmpeg, url: https://github.com/FFmpeg/FFmpeg
    # need install cpulimit, url: https://github.com/opsengine/cpulimit
    def perform(url = nil)
      # 以此影片為範例,出處: Videvo
      url = 'https://cdn.videvo.net/videvo_files/video/free/2013-05/originalContent/DigitalCountdownTimerVidevo.mov'
      video_name = parse_video_name(url)
      video_file_path(video_name)
      download_video(url)
      converter
    rescue StandardError => e
      logger.error "[Video::HandleVideoWorker] ERROR:\n #{e.inspect}\n #{e.backtrace}"
    end

    private

    def logger
      FileLog.logger('worker/video/video_worker.log')
    end

    def parse_video_name(url)
      url.split('/')[-1] # "DigitalCountdownTimerVidevo.mov"
    end

    def video_file_path(video_name)
      @input_file = VIDEO_PATH.join(video_name)
      mp4_format = video_name.split('.')[0] + '.mp4'
      @output_file = VIDEO_PATH.join("converted-#{mp4_format}")
    end

    def download_video(url)
      resp = HTTP.get(url)
      save_origin_video(resp)
    end

    def save_origin_video(video_response)
      FileUtils.mkdir_p(VIDEO_PATH)
      File.write(@input_file, video_response.to_s.force_encoding('UTF-8'))
    end

    def converter
      priority = 'nice -n 20 cpulimit -l 80' # cpulimit: 限制 CPU usage (目前上限設 80%)
      ffmpeg_threads = 'ffmpeg -threads 2'   # ffmpeg -threads: 設定 CPU 核心數 (目前設定 2)
      `#{priority} -i #{ffmpeg_threads} -i #{@input_file} #{@output_file}`
    end
  end
end

指令範例 (tldr)

在 Linux 文章系列,有提到 tldr ,非常實用

tldr ffmpeg

# ---

ffmpeg

Video conversion tool.
More information: <https://ffmpeg.org>.

- Extract the sound from a video and save it as MP3:
    ffmpeg -i video.mp4 -vn sound.mp3

- Convert frames from a video or GIF into individual numbered images:
    ffmpeg -i video.mpg|video.gif frame_%d.png

- Combine numbered images (frame_1.jpg, frame_2.jpg, etc) into a video or GIF:
    ffmpeg -i frame_%d.jpg -f image2 video.mpg|video.gif

- Quickly extract a single frame from a video at time mm:ss and save it as a 128x128 resolution image:
    ffmpeg -ss mm:ss -i video.mp4 -frames 1 -s 128x128 -f image2 image.png

- Trim a video from a given start time mm:ss to an end time mm2:ss2 (omit the -to flag to trim till the end):
    ffmpeg -ss mm:ss -to mm2:ss2 -i video.mp4 -codec copy output.mp4

- Convert AVI video to MP4. AAC Audio @ 128kbit, h264 Video @ CRF 23:
    ffmpeg -i input_video.avi -codec:audio aac -b:audio 128k -codec:video libx264 -crf 23 output_video.mp4

- Remux MKV video to MP4 without re-encoding audio or video streams:
    ffmpeg -i input_video.mkv -codec copy output_video.mp4

- Convert MP4 video to VP9 codec. For the best quality, use a CRF value (recommended range 15-35) and -b:video MUST be 0:
    ffmpeg -i input_video.mp4 -codec:video libvpx-vp9 -crf 30 -b:video 0 -codec:audio libopus -vbr on -threads number_of_threads output_video.webm

更多指令

ffmpeg -h


ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 11.0.3 (clang-1103.0.32.62)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...

Getting help:
    -h      -- print basic options
    -h long -- print more options
    -h full -- print all options (including all format and codec specific options, very long)
    -h type=name -- print all options for the named decoder/encoder/demuxer/muxer/filter/bsf/protocol
    See man ffmpeg for detailed description of the options.

Print help / information / capabilities:
-L                  show license
-h topic            show help
-? topic            show help
-help topic         show help
--help topic        show help
-version            show version
-buildconf          show build configuration
-formats            show available formats
-muxers             show available muxers
-demuxers           show available demuxers
-devices            show available devices
-codecs             show available codecs
-decoders           show available decoders
-encoders           show available encoders
-bsfs               show available bit stream filters
-protocols          show available protocols
-filters            show available filters
-pix_fmts           show available pixel formats
-layouts            show standard channel layouts
-sample_fmts        show available audio sample formats
-colors             show available color names
-sources device     list sources of the input device
-sinks device       list sinks of the output device
-hwaccels           show available HW acceleration methods

Global options (affect whole program instead of just one file):
-loglevel loglevel  set logging level
-v loglevel         set logging level
-report             generate a report
-max_alloc bytes    set maximum size of a single allocated block
-y                  overwrite output files
-n                  never overwrite output files
-ignore_unknown     Ignore unknown stream types
-filter_threads     number of non-complex filter threads
-filter_complex_threads  number of threads for -filter_complex
-stats              print progress report during encoding
-max_error_rate maximum error rate  ratio of errors (0.0: no errors, 1.0: 100% errors) above which ffmpeg returns an error instead of success.
-bits_per_raw_sample number  set the number of bits per raw sample
-vol volume         change audio volume (256=normal)

Per-file main options:
-f fmt              force format
-c codec            codec name
-codec codec        codec name
-pre preset         preset name
-map_metadata outfile[,metadata]:infile[,metadata]  set metadata information of outfile from infile
-t duration         record or transcode "duration" seconds of audio/video
-to time_stop       record or transcode stop time
-fs limit_size      set the limit file size in bytes
-ss time_off        set the start time offset
-sseof time_off     set the start time offset relative to EOF
-seek_timestamp     enable/disable seeking by timestamp with -ss
-timestamp time     set the recording timestamp ('now' to set the current time)
-metadata string=string  add metadata
-program title=string:st=number...  add program with specified streams
-target type        specify target file type ("vcd", "svcd", "dvd", "dv" or "dv50" with optional prefixes "pal-", "ntsc-" or "film-")
-apad               audio pad
-frames number      set the number of frames to output
-filter filter_graph  set stream filtergraph
-filter_script filename  read stream filtergraph description from a file
-reinit_filter      reinit filtergraph on input parameter changes
-discard            discard
-disposition        disposition

Video options:
-vframes number     set the number of video frames to output
-r rate             set frame rate (Hz value, fraction or abbreviation)
-s size             set frame size (WxH or abbreviation)
-aspect aspect      set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
-bits_per_raw_sample number  set the number of bits per raw sample
-vn                 disable video
-vcodec codec       force video codec ('copy' to copy stream)
-timecode hh:mm:ss[:;.]ff  set initial TimeCode value.
-pass n             select the pass number (1 to 3)
-vf filter_graph    set video filters
-ab bitrate         audio bitrate (please use -b:a)
-b bitrate          video bitrate (please use -b:v)
-dn                 disable data

Audio options:
-aframes number     set the number of audio frames to output
-aq quality         set audio quality (codec-specific)
-ar rate            set audio sampling rate (in Hz)
-ac channels        set number of audio channels
-an                 disable audio
-acodec codec       force audio codec ('copy' to copy stream)
-vol volume         change audio volume (256=normal)
-af filter_graph    set audio filters

Subtitle options:
-s size             set frame size (WxH or abbreviation)
-sn                 disable subtitle
-scodec codec       force subtitle codec ('copy' to copy stream)
-stag fourcc/tag    force subtitle tag/fourcc
-fix_sub_duration   fix subtitles duration
-canvas_size size   set canvas size (WxH or abbreviation)
-spre preset        set the subtitle options to the indicated preset

小結

會發現影像處理,其實蠻有趣的,許多參數說明都是帶過,以實用為主,若對各參數細節調整有興趣,再自行 Google,FFmpeg 相關的文章挺多的,中文的資料也不少可參考,若想在 rails console 中執行 Linux 指令,可使用以下三種方法

[1] pry(main)> system("echo 我是小菜")
我是小菜
true
[2] pry(main)> `echo 我是小菜`
"我是小菜\n"
[3] pry(main)> .echo '我是小菜'
我是小菜


鐵人賽文章連結:https://ithelp.ithome.com.tw/articles/10247454
medium 文章連結:https://link.medium.com/Z5b8hjxVdab
本文同步發布於 小菜的 Blog https://riverye.com/

備註:之後文章修改更新,以個人部落格為主


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Day25 - Ruby on Rails 中的 Sidekiq 的介紹與應用
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Day27 - Ruby on Rails 中使用 Foreman 打包所有要啟動的 server
系列文
Ruby on Rails 與它們相關的東西31

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