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• How to calculate the "Range" header for mp4 file to play/download a part of it ? [youtube-dl]

  5 décembre 2016, par supersan

  I’m using youtube-dl to download videos from YouTube. Unfortunately, sometimes I just need to download a part of the video like 10 seconds of a 3 hour video and here is how I see I can do it.

  Step 1 : Get the URL of the mp4 file from youtube-dl.

  youtube-dl -g -f "[ext=mp4]" https://www.youtube.com/watch?v=qOZ1u9VpoMk

  This returns $url : the full URL of mp4 file on server.

  Step 2 : Download part of the video using curl

  curl -r $startBytes-$endBytes $url

  But how to calculate $startBytes and $endBytes. What is the formula for that ?

  P.S I was thinking could be something as simple but this isn’t it..

  $startBytes = (total_size_of_video / total_length_of_video_secs) * start_seconds

  P.P.S. When I play the mp4 video in Chrome and use the scrub bar to jump around in the video, Chrome too send the Range header to the same URL (as I can see in fiddler)

• FFMPEG : Youtube streaming quality and speed issues

  25 février 2020, par Alex Paramonov

  I am trying to make a reliable stream from my Icecast/Shoutcast servers to Youtube live. The command that I use is :

  ffmpeg -v verbose -framerate 30 -loop 1 -i /var/image.jpg -re -i http://127.0.0.1:4700/radio -c:v libx264 -preset ultrafast -b:v 2250k -maxrate 6000k -bufsize 6000k -c:a copy -ab 128k -s 1920x1080 -framerate 30 -g 60 -keyint_min 60 -f flv  rtmp://a.rtmp.youtube.com/live2/xxx

  As you can see I am using recommended bitrate for Youtube, insert keyframes every 2 seconds and streaming at 30 frames per second.
  The stream is working but after running for some time two thing are happening :

  1. FFMPEG speed falls from 1x to something like 0.998x
  2. Youtube starts complaining that video stream speed is slow, markes the quality as bad and sometimes video starts buffering.

  Why is this happening ? CPU load is normal, connectivity is ok (the stream is running on a 1Gg/s dedicated server).

  Since in my example above I am streaming a single image as a logo of the stream I also tried to generate a short 30 seconds video with that image and broadcast that video instead of an image, but that did not help as well.

  The command I used for conversion :

  ffmpeg -framerate 30 -loop 1 -i /var/image.jpg -c:v libx264 -preset ultrafast -tune stillimage  -b:v 2250k -minrate 2250k -maxrate 6000k -bufsize 6000k -framerate 30 -g 60 -keyint_min 60 -t 30 out4.mp4

  And broadcast with

  ffmpeg -stream_loop -1 -i out4.mp4  -re -i http://127.0.0.1:4700/radio -c:v copy -c:a copy  -framerate 30 -g 60 -keyint_min 60 -f flv  rtmp://a.rtmp.youtube.com/live2/xxx

  ffmpeg version is 4.1.1

• ffmpeg streaming to youtube slow

  1er avril 2017, par boygiandi

  I’m trying to send a video file to youtube as livestreaming. The stream command look like this

  ffmpeg -re -i "/tmp/4745.mkv" -acodec aac -pix_fmt yuv420p -bufsize 6000k -vb 400k -maxrate 1500k -deinterlace -vcodec libx264 -preset fast -g 60 -r 30 -crf 1 -f flv "rtmp ://...."

  The last line of output log look like this

  [ sh : 2017-04-01 7:19:54 ]size= 242706kB time=00:21:08.11 bitrate=1567.9kbits/s speed=0.882x

  As I understand, the speed=0.882x mean it send data to youtube slower than expected ( 1x mean streaming fine, lower mean buffering ). I tried to change some params of ffmpeg command, like change -preset fast to superfast, ultrafast : it faster but quality very bad and I still can’t control the out put speed. Sometime it’s 1x, sometime lower.
  Note that I run more than 1 ffmpeg instants at the same time, it may problem of CPU, RAM or Network, I checked them all.

  • CPU 40% ( top command )
  • RAM used 3Gb/7Gb
  • Network upload Avg : 8.45 MBit/s ( Max Upload : 70.76 Mbit/s - speedtest )

  So I don’t know what’s problem. Anyone can help ?