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• FFmpeg - selecting appropriate bitrate for VP9 encoding

  6 avril 2017, par fastily

  I am looking to encode a 4k video shot with iPhone 6s in VP9 in the best quality possible.

  For reference, stream data of the video I would like to encode, via ffprobe :

  Duration: 00:00:10.48, start: 0.000000, bitrate: 46047 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 3840x2160, 45959 kb/s, 29.98 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 79 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler

  I am using the following FFmpeg commands, based on these instructions (see Best Quality (Slowest) Recommended Settings section).

  1. ffmpeg -i INPUT.mov -c:v libvpx-vp9 -pass 1 -b:v 46000K -threads 4 -speed 4 -g 9999 -an -f webm -y /dev/null
  2. ffmpeg -I INPUT.mov -c:v libvpx-vp9 -pass 2 -b:v 46000K -threads 4 -speed 0 -g 9999 -an -f webm OUTPUT.webm

  Is there a best practice to select an optimal -b:v value such that the resulting video is visually indistinguishable from the original ? I have tried values ranging from 36000K-46000K, but these result in massive files with an overall bitrate exceeding the target bitrate.

  Thanks in advance !

• Paperclip geometry ignored

  27 mars 2017, par ACIDSTEALTH

  I have a model called Snapshot, which represents a user-recorded video. I want to take the input video file and scale it to fit within a 720x720 box (ImageMagick documentation). I then want to capture some screenshots of the video to represent it in my app. These sizes are specified accordingly in my model.

  I expect the output of this to be an original video with a maximum width of 720px (assuming it was recorded in landscape mode), a large JPG image with a maximum width of 540px, etc.

  When I attach the video file and save the model, the images and video file are processed but the result is not what I expected. The video file has a resolution of 960x720 and the images are all square (540x540, 360x360, etc).

  I’m not sure if I’m doing something wrong or if this is just a bug with Paperclip. Here is my code :

  class Snapshot < ApplicationRecord
  
      has_attached_file :video,
  
          styles: {
  
              original: { geometry: "720x720", format: 'mp4' },
  
              large: { geometry: "540x540", format: 'jpg' },
  
              medium: { geometry: "360x360", format: 'jpg' },
  
              thumb: { geometry: "180x180", format: 'jpg' }
  
          },
  
          default_url: "", processors: [:transcoder]
  
      validates_attachment_content_type :video, content_type: /\Avideo\/.*\Z/
  
      validates_attachment_size :video, less_than: 100.megabytes
  
  end

  I have also tried adjusting the geometry to 720x720>, 540x540>, etc. When I did this, the attachments’ resolution was unchanged, which seems to go completely against my understanding of how ImageMagick geometry works. I have numerous other models with image-only attachments that do not suffer from this issue.

  Here is a snippet from my Gemfile.lock so you can see which versions I am running :

  delayed_paperclip (3.0.1)
  
    activejob (>= 4.2)
  
    paperclip (>= 3.3)
  
  paperclip (5.1.0)
  
    activemodel (>= 4.2.0)
  
    activesupport (>= 4.2.0)
  
    cocaine (~> 0.5.5)
  
    mime-types
  
    mimemagic (~> 0.3.0)
  
  paperclip-av-transcoder (0.6.4)
  
    av (~> 0.9.0)
  
    paperclip (>= 2.5.2)
  
  paperclip-optimizer (2.0.0)
  
    image_optim (~> 0.19)
  
    paperclip (>= 3.4)

  Update
  I retried this with a video recorded in portrait mode (iPhone 6 front-facing webcam) and the video file’s output size was 720x720. The images were still square as before.

• ffmpeg override the same file for every second of the video [on hold]

  5 février 2017, par Dorin Pleava

  I want to get one image for every 10 seconds from a livestream/video, but the image should have the same name, meaning I want to override it every cycle.

  This is my command :

  ffmpeg.exe -i http://iphone-streaming.ustream.tv/uhls/17074538/streams/live/iphone/playlist.m3u8 -bt 20M -s 480x300 -vf fps=1/10 -y photo.jpg

  This code works for one image but for the next I get this

  "Could not get frame filename number 2 from pattern ’photo.jpg’ (either set updatefirst or use a pattern like %03d within the filename pattern)
  av_interleaved_write_frame() : Invalid argument"

  If I replace photo.jpeg with photo%03d.jpg I get photo001.jpec, followed by photo002.jpeg, etc.