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• avcodec/nvenc : De-compensate aspect ratio compensation of DVD-like content.

  28 janvier 2015, par Philip Langdale

  avcodec/nvenc : De-compensate aspect ratio compensation of DVD-like content.
  For reasons we are not privy to, nvidia decided that the nvenc encoder
  
  should apply aspect ratio compensation to ’DVD like’ content, assuming that
  
  the content is not bt.601 compliant, but needs to be bt.601 compliant. In
  
  this context, that means that they make the following, questionable,
  
  assumptions :
  1) If the input dimensions are 720x480 or 720x576, assume the content has
  
  an active area of 704x480 or 704x576.
  2) Assume that whatever the input sample aspect ratio is, it does not account
  
  for the difference between ’physical’ and ’active’ dimensions.
  From, these assumptions, they then conclude that they can ’help’, by adjusting
  
  the sample aspect ratio by a factor of 45/44. And indeed, if you wanted to
  
  display only the 704 wide active area with the same aspect ratio as the full
  
  720 wide image - this would be the correct adjustment factor, but what if you
  
  don’t ? And more importantly, what if you’re used to ffmpeg not making this kind
  
  of adjustment at encode time - because none of the other encoders do this !
  And, what if you had already accounted for bt.601 and your input had the
  
  correct attributes ? Well, it’s going to apply the compensation anyway !
  
  So, if you take some content, and feed it through nvenc repeatedly, it
  
  will keep scaling the aspect ratio every time, stretching your video out
  
  more and more and more.
  So, clearly, regardless of whether you want to apply bt.601 aspect ratio
  
  adjustments or not, this is not the way to do it. With any other ffmpeg
  
  encoder, you would do it as part of defining your input paramters or
  
  do the adjustment at playback time, and there’s no reason by nvenc
  
  should be any different.
  This change adds some logic to undo the compensation that nvenc would
  
  otherwise do.
  nvidia engineers have told us that they will work to make this
  
  compensation mechanism optional in a future release of the nvenc
  
  SDK. At that point, we can adapt accordingly.
  Signed-off-by : Philip Langdale <philipl@overt.org>
  
  Reviewed-by : Timo Rothenpieler <timo@rothenpieler.org>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/nvenc.c

• cross-platform syntax for mp4 embedded in html5

  11 janvier 2015, par CodeMed

  The code below produces a properly embedded video in firefox, but does not display properly in internet explorer or in android. I have all my browsers set to automatically update, so they are all always running the most current versions.

  In `internet explorer`, the code below leaves a large blank space where the  
  
  video should be.  The user has to hover over the large blank space before the  
  
  controls become visible.  
  
  
  
  In `android`, the code below produces an unusable/unclickable area, and the  
  
  user has to greatly zoom the focus to get the small start button to become  
  
  big enough to click to start the video.  
  
  
  
  However, in `firefox`, the code below shows the first frame of the video,  
  
  which you can click to start the video.  

  How can I change the code below to get all three of these browsers to show the first frame when the page loads, and for the video to be start-able when the user clicks on the first frame ?

  Here is a link to the video file on a file sharing site.

  Here is the ffmeg code for processing the video :

  ffmpeg -y -i SourceFile.mp4 -s 1280x720 -c:v libx264 -b 3M -strict -2 -movflags faststart DestFile.mp4

  Thanks to offbeatmammal for getting me this far.
  Here is the html5 code for embedding the video in a web page browser :

  <video width="640" height="480" controls="controls">
  
      <source src="somefile.mp4" type="video/mp4">
  
      Your browser does not support the video tag.
  
  </source></video>

• avdevice/xcbgrab : Fix show_region rectangle

  7 décembre 2014, par Daniel Moran

  avdevice/xcbgrab : Fix show_region rectangle
  Fixes trac ticket #4164
  This is to address an error when using show_region, which would cause part of the captured area to become static.
  
  It looks like the rectangle specifying the capture area was relative to the capture window.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavdevice/xcbgrab.c