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• YouTube's HD Video Streaming Server Technology ?

  30 septembre 2013, par bgentry

  Lately I've been researching different methods for streaming MP4s to the browser. Flash Media Server is an obvious choice here (using Cloudfront), and most solutions I've seen use the RTMP protocol.

  However, I spent some time on YouTube with Firebug and Chrome debugger figuring out how their streaming worked and I discovered some interesting differences between some of their videos and quality rates.

  My two sample videos are A and B. A is available up to 480p and B is available up to 1080p. For both videos, all rates up to 480p are served in an FLV container with H.264 video and AAC audio, over HTTP. What's interesting here is that if you have not yet downloaded (cached) the entire video, and you try to skip forward to an uncached part of the video, a new request will be made with a 'begin' parameter equal to the target offset in milliseconds. Example from Video A at 480p :

  http://v11.lscache8.c.youtube.com/videoplayback?ip=0.0.0.0&sparams=id%2Cexpire%2Cip%2Cipbits%2Citag%2Calgorithm%2Cburst%2Cfactor%2Coc%3AU0dWTldQVF9FSkNNNl9PSlhJ&fexp=904806%2C902906%2C903711&algorithm=throttle-factor&itag=35&ipbits=0&burst=40&sver=3&expire=1279756800&key=yt1&signature=D2D704D63C242CF187CAA5B5D5BAFB8DFACAC5FF.39180C01559C976717B651A7EB1D0C6249231EB7&factor=1.25&id=8568eb3135971f6f&begin=111863
  
  
  
  Response Headers:
  
  Cache-Control:public,max-age=23472
  
  Connection:close
  
  Content-Length:14320637
  
  Content-Type:video/x-flv
  
  Date:Wed, 21 Jul 2010 17:23:48 GMT
  
  Expires:Wed, 21 Jul 2010 23:55:00 GMT
  
  Last-Modified:Wed, 19 May 2010 12:31:41 GMT
  
  Server:gvs 1.0
  
  X-Content-Type-Options:nosniff

  The file returned by this URL is a fully valid FLV containing only the portion of the video after the requested offset.

  I did the same kind of test on the higher resolution versions of Video B. At 720p and 1080p, YouTube will return a video in an MP4 container, also with H.264 video and AAC audio. What's impressive to me is that their server takes the same type of offset for an MP4 video (via the 'begin' parameter) and returns a valid, streamable MP4 (moov atom at the front of the file with correct offsets) that also only includes the requested portion of the video.

  So, how does YouTube do this ? How do they generate the FLV or MP4 container on the fly with the correct headers and only the desired segment of the requested video ? I know this can be accomplished using FFMPEG to seek to the desired start point and the qt-faststart script to reposition the moov atom to the front of the stream, but it seems like this would be too slow to handle on-demand for millions of YouTube viewers.

  Ideas ?

  Thanks in advance !

  Footnote : I am not allowed to include more than 1 link at this point, so here is Video A's URL : http:// www.youtube .com/watch ?v=hWjrMTWXH28 "Video available up to 480p"

• How easy is it to create a YouTube to MP3 application using yt-dlp and ffmpeg ?

  26 juin 2022, par fowlis

  I was thinking I could automate the process of downloading a video and converting it to mp3 (or other formats).
  
Instead of doing the process myself (which doesn't take that long and isn't too much hassle), which looks something like this :
  
• yt-dlp https://www.youtube.com/watch?v=dQw4w9WgXcQ
  
• wait for download then (find and) rename file to something simpler for next command
  
• ffmpeg -i video.mp4 video.mp3

  

  


  I thought I could turn it into a simple JS (or other language) program instead, where it :
  

  


  

  1. Asks for link and what format I want it in

  


  2. Downloads the video

  


  3. Renames it (not sure how easy this is)

  


  4. Turns it into requested format

  


  5. Opens file location

  


  


  If something like this is possible, please let me know some things I should know since I've never written a windows app before, and some general guidance for how I could do this.

  
I apologise if questions like this aren't exactly allowed on this site, its my first time posting too.
  
Thanks in advance !

  


• How to yt-dlp extract youtube audio-only to 32-bit float 48000 .wav ? [closed]

  28 avril 2024, par Rowe Morehouse

  My use case : Extract just the audio from a youtube URL directly to a .wav at 32-bit float 48000.

  


  Preferably without any post process args or secondary passes or after-the-fact conversion or muxing.

  


  I want f32le, aka PCM_f32le, aka PCM 32-bit floating-point little-endian, which is supported by ffmpeg. Also want 48000 sample rate, as stated.

  


  Is this possible ?

  


  My current command :

  


  yt-dlp -f bestaudio --extract-audio --audio-format wav --audio-quality 0


  


  What do I need to add to achieve my use case / job-to-be-done ??