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• Playing video with transparency in iOS

  14 juillet 2020, par 0Ds0

  A bit of background, i want to play videos with transparency on the web converted from gifs, for all non apple devices i can easily export a webm file like so

  


  ffmpeg -i test.gif -c:v libvpx-vp9 -qmin 0 -qmax 18 -crf 9 -b:v 1400K -quality good -cpu-used 0 -auto-alt-ref 0 -pix_fmt yuva420p -an -sn  -metadata title="test webm" test.webm

  


  No need for video streaming with HTTP response 206 partial content loaded it works out of the box

  


  Now for safari and apple devices i am presented with a totally different beast i set up a endpoint that serves the video with HTTP 206 responses and after a quite a struggle i can have the same end result for Safari in macOSX, and i convert the videos like so

  


  ffmpeg -i test.gif -qmin 0 -qmax 18  -vcodec prores_ks -q:v 64 -b:v 1400K  -pix_fmt yuva444p10le -profile:v 4444 -an -sn -metadata title="test mov" test.mov

  


  I put in the url address bar the that serves the video with stream and the video plays with transparency all good.

  


  Now on Safari in iOS the video just does not play, it is loaded with the same endpoint and other videos without transparency also work, serving from the same stream endpoint.

  


  Does anyone knows of a solution to encode a video with transparency that plays on all apple devices ?

  


  I also gave handbrake a try without success, actually could not even get the transparency right with handbrake.

  


• Need help understanding this script which uses ffmpeg to send rtmp input to node.js script

  4 juin 2022, par Arpit Shukla

  I was trying to understand this shell script which uses ffmpeg to take an rtmp input stream and send it to a node.js script. But I am having trouble understanding the syntax. Can someone please explain what is going on here ?

  


  The script :

  


  while :
do
  echo "Loop start"

  feed_time=$(ffprobe -v error -show_entries format=start_time -of default=noprint_wrappers=1:nokey=1 $RTMP_INPUT)
  printf "feed_time value: ${feed_time}"

  if [ ! -z "${feed_time}" ]
  then
  ffmpeg -i $RTMP_INPUT -tune zerolatency -muxdelay 0 -af "afftdn=nf=-20, highpass=f=200, lowpass=f=3000" -vn -sn -dn -f wav -ar 16000 -ac 1 - 2>/dev/null | node src/transcribe.js $feed_time

  else
  echo "FFprobe returned null as a feed time."
  
  fi

  echo "Loop finish"
  sleep 3
done


  


  

  • What is feed_time here ? What does it represent ?

  


  • What is this portion doing - 2>/dev/null | node src/transcribe.js $feed_time ?

  


  • What is the use of sleep 3 ? Does this mean that we are sending audio stream to node.js in chuncks of 3 seconds ?

  


  


• Imageio python converts GIF to MP4 incorrectly

  1er juin 2018, par Apurva Koti

  I am writing a function to speed up/down a given GIF (or .gifv) file, and save the resulting animation as an .mp4 file.

  I’m using the python imageio package (and its ffmpeg plugin) to do this - download the raw binary data from the gif, write each frame to an mp4, and set the fps of the mp4 to whatever.

  My code is -

  def changespeed(vid, mult):
  
      vid = vid.replace('.gifv', '.gif')
  
      data = urllib2.urlopen(vid).read()
  
      reader = imageio.get_reader(data, 'gif')
  
      dur = (float(reader.get_meta_data()['duration']))
  
      oldfps = 1000.0 / (10 if dur == 0 else dur)
  
  
  
  
  
      writer = imageio.get_writer('output.mp4', fps=(oldfps*mult), quality=8.0)
  
  
  
      for frame in reader:
  
          writer.append_data(frame)
  
      writer.close()

  The problem is, at times the output colors will be heavily corrupted, and there doesn’t seem to be any predictability. This happens with some gifs and doesn’t happen with others. I have tried setting a high quality parameter in the writer but this doesn’t help.

  Here is an example of a problematic GIF -

  Input : https://i.imgur.com/xFezNYK.gif

  Output : https://giant.gfycat.com/MelodicShimmeringBarb.mp4

  I can see this issue locally in output.mp4, so the issue isn’t with uploading to Gfycat.

  Is there anything I can do to avoid this behavior ? Thanks.