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• What ffmpeg output format (-f) do I use for two-pass encoding of mkv files

  16 mai 2020, par Mav-Tek

  I recently backed up one of my Blu-ray movies and it is about 36 GB. Using ffmpeg to get info from the video, it is in h.264 in an mkv container. I want to shrink the file size using h.265 compression and targeting a bitrate of 4 Mbits/s so that I can stream it while I am away from my home over my Plex server. My upload speed is limited to 5 Mb/s.

  



  Although I could easily do this with simple software, I want to learn more coding. I have found the proper ffmpeg code two do a two-pass encoding, but in all examples I have found, they use an output format of mp4 but state that "you need to specify an output format (with -f) that matches the output format you will use in pass 2." I assume my "output format" is mkv, but that does not allow my code to run. Can someone explain to me what is meant by output format and what I should be using to encode this from h264 to h265 in a mkv container ?

  



  ffmpeg -y -i input.mkv -c:v libx265 -b:v 4M -x265-params pass=1 -an -f mkv /dev/null && \ ffmpeg -i "Arrival (2016).mkv" -c:v libx265 -b:v 4M -x265-params pass=2 -c:a copy output.mkv 


  



  Also, in order to make this work on my windows PC, I am trying to learn how to edit some of the arguments to allow it to work in Powershell. I believe this is how I would do that :

  



  (ffmpeg -y -i input.mkv -c:v libx265 -b:v 4M -x265-params pass=1 -an -f mkv NUL) -AND (^ ffmpeg -i "Arrival (2016).mkv" -c:v libx265 -b:v 4M -x265-params pass=2 -c:a copy  output.mkv)


  


• How to send continuous stream of frames to server most efficiently

  27 avril 2019, par Duthopi

  I am trying to send frames from a local camera (raspberry pi camera, but could also be my laptop’s webcam) to a Google cloud instance, on which I am running AI processing of the frames.

  I am managing to send frames captured through opencv via http (i.e. tcp ??) and receiving them on a flask server. When the flask server is running locally I can get good fps (50+ fps for image size 640x480), however once I send the frames to a flask app on the google instance the fps drop drastically to 5fps.

  How I currently send frames :

  while True:
  
          frame = vs.read() #Separate thread, using cv2 to get the frame
  
  
  
          ret, jpeg = cv2.imencode('.jpg', frame)
  
          imgdata = jpeg.tobytes()
  
          response = requests.post(
  
              url='http://<ip address="address" of="of" google="google" instance="instance">:<port>',
  
              data= imgdata,
  
              headers={'content-type':'image/jpeg'},
  
              )
  
  </port></ip>

  I see two problems with this :
  1 - using tcp means I am slower than udp protocol, however udp is limited in byte size. Correct me if I am wrong, but it seems very complex to send truncated frames and put them back together on the server..
  2 - Even if I had udp working, there is no compression of frames, so I will never reach an efficient transfer

  I expect the answer to be something like using ffmpeg, but so far I only figured out how to stream frames on a local port with ffmpeg, I do not know if it is possible to send frames to a remote server.

  Any recommendations on the best way forward ?

• Amazon S3 : how to combine all images into a video ?

  17 mars 2015, par scientiffic

  I’m in my Rails app, I enable users to upload images, which get processed using ffmpeg to create a video slideshow.

  I have this working locally, but am wondering how to do this when deploying the app using Heroku. In particular, I know Heroku has limited storage and has a read-only filesystem, so using Carrierwave without S3 or an external storage option doesn’t seem like an option.

  But how would I run a task like the following using S3, where I combine all images into a video ?

  The ffmpeg command is

  ffmpeg -r 5 -i https://s3.amazonaws.com/[]/uploads/image/image_file/26/img%03d.jpg output.mp4 -y

  And the AWS "folder" contains the following :
  https://s3.amazonaws.com/[]/uploads/image/image_file/26/img001.jpg
  https://s3.amazonaws.com/[]/uploads/image/image_file/26/img002.jpg
  https://s3.amazonaws.com/[]/uploads/image/image_file/26/img003.jpg

  When I try to do the following, I get an error with ffmpeg not knowing what to do with :

  https://s3.amazonaws.com/[]/uploads/image/image_file/26/img%03d.jpg

  Note, this whole video compilation process works fine for me locally, so I know in theory it should work.