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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"

• Merge remote-tracking branch ’cehoyos/master’

  4 septembre 2013, par Michael Niedermayer

  Merge remote-tracking branch ’cehoyos/master’
  * cehoyos/master :
  
    Show subtitle resolution in avcodec_string().
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/utils.c

• FFMPEG wmv conversion to flv

  25 novembre 2012, par Brandon Grossutti

  anyone using ffmpeg

  I have a fairly simple wmv exported by a user from movie maker with standard output and want to convert to .flv using

  C :>ffmpeg -i "E :\Jab Core 4 Recounters.wmv" -vcodec flv "C :\Net Projects\SVN\IntegratedAlgorithmics\src\MediaAdmin\MediaAdmin\bin\Debug\Movies\Jab Core 4 Recounters.flv" -ar 44100

  the output / error i receive is

  FFmpeg version 0.5, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  
    configuration: --enable-gpl --enable-postproc --enable-swscale --enable-avfilt
  
  er --enable-avfilter-lavf --enable-pthreads --enable-avisynth --enable-libfaac -
  
  -enable-libfaad --enable-libmp3lame --enable-libspeex --enable-libtheora --enabl
  
  e-libvorbis --enable-libxvid --enable-libx264 --enable-memalign-hack
  
    libavutil     49.15. 0 / 49.15. 0
  
    libavcodec    52.20. 0 / 52.20. 0
  
    libavformat   52.31. 0 / 52.31. 0
  
    libavdevice   52. 1. 0 / 52. 1. 0
  
    libavfilter    0. 4. 0 /  0. 4. 0
  
    libswscale     0. 7. 1 /  0. 7. 1
  
    libpostproc   51. 2. 0 / 51. 2. 0
  
    built on Mar 16 2009 16:09:18, gcc: 4.2.4 [Sherpya]
  
  [wmv3 @ 0x1c0d490]Extra data: 8 bits left, value: 0
  
  
  
  Seems stream 1 codec frame rate differs from container frame rate: 1000.00 (1000
  
  /1) -> 30.00 (30/1)
  
  Input #0, asf, from 'E:\Jab Core 4 Recounters.wmv':
  
    Duration: 00:01:55.99, start: 5.000000, bitrate: 813 kb/s
  
      Stream #0.0: Audio: wmav2, 48000 Hz, stereo, s16, 192 kb/s
  
      Stream #0.1: Video: wmv3, yuv420p, 640x480, 586 kb/s, 30 tbr, 1k tbn, 1k tbc
  
  
  
  Output #0, flv, to 'C:\Net Projects\SVN\IntegratedAlgorithmics\src\MediaAdmin\Me
  
  diaAdmin\bin\Debug\Movies\Jab Core 4 Recounters.flv':
  
      Stream #0.0: Video: flv, yuv420p, 640x480, q=2-31, 200 kb/s, 90k tbn, 30 tbc
  
  
  
      Stream #0.1: Audio: libmp3lame, 48000 Hz, stereo, s16, 64 kb/s
  
  Stream mapping:
  
    Stream #0.1 -> #0.0
  
    Stream #0.0 -> #0.1
  
  [wmv3 @ 0x1c0d490]Extra data: 8 bits left, value: 0
  
  [libmp3lame @ 0x1c0d8d0]flv does not support that sample rate, choose from (4410
  
  0, 22050, 11025).
  
  Could not write header for output file #0 (incorrect codec parameters ?)

  i added th -ar switch when i got the error the first time

  the codec info i have on the file is as follows

  General
  
  Complete name                    : E:\Jab Core 4 Recounters.wmv
  
  Format                           : Windows Media
  
  File size                        : 11.3 MiB
  
  Duration                         : 2mn 0s
  
  Overall bit rate mode            : Variable
  
  Overall bit rate                 : 780 Kbps
  
  Maximum Overall bit rate         : 949 Kbps
  
  Encoded date                     : UTC 2009-03-07 07:02:41.121
  
  Writing application              :  6.0.6000.16386 / Windows Movie Maker
  
  Application                      : Windows Movie Maker 6.0.6000.16386
  
  
  
  Video
  
  ID                               : 2
  
  Format                           : VC-1
  
  Format profile                   : MP@ML
  
  Codec ID                         : WMV3
  
  Codec ID/Info                    : Windows Media Video 9
  
  Codec ID/Hint                    : WMV3
  
  Duration                         : 2mn 0s
  
  Bit rate mode                    : Variable
  
  Bit rate                         : 587 Kbps
  
  Width                            : 640 pixels
  
  Height                           : 480 pixels
  
  Display aspect ratio             : 4/3
  
  Frame rate                       : 30.000 fps
  
  Resolution                       : 24 bits
  
  Scan type                        : Progressive
  
  Bits/(Pixel*Frame)               : 0.064
  
  Stream size                      : 8.46 MiB (75%)
  
  Language                         : en-us
  
  
  
  Audio
  
  ID                               : 1
  
  Format                           : WMA2
  
  Format profile                   : L3
  
  Codec ID                         : 161
  
  Codec ID/Info                    : Windows Media Audio 2
  
  Description of the codec         : Windows Media Audio 9.2 - VBR Quality 90, 48 kHz, stereo 1-pass VBR
  
  Duration                         : 2mn 0s
  
  Bit rate mode                    : Variable
  
  Bit rate                         : 186 Kbps
  
  Channel(s)                       : 2 channels
  
  Sampling rate                    : 48.0 KHz
  
  Resolution                       : 16 bits
  
  Stream size                      : 2.68 MiB (24%)
  
  Language                         : en-us

  i see alot of people with this issue with so solution or cause

  any ideas would be helpful
  thanks in advance