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• How To Play Hardware Accelerated Video on A Mac

  28 mai 2013, par Multimedia Mike — General

  I have a friend who was considering purchasing a Mac Mini recently. At the time of this writing, there are 3 desktop models (and 2 more “server” models).

  
  
  

  The cheapest one is a Core i5 2.5 GHz. Then there are 2 Core i7 models : 2.3 GHz and 2.6 GHz. The difference between the latter 2 is US$100. The only appreciable technical difference is the extra 0.3 GHz and the choice came down to those 2.

  He asked me which one would be able to play HD video at full frame rate. I found this query puzzling. But then, I have been “in the biz” for a bit too long. Whether or not a computer or device can play a video well depends on a lot of factors.

  Hardware Support
  First of all, looking at the raw speed of the general-purpose CPU inside of a computer as a gauge of video playback performance is generally misguided in this day and age. In general, we have a video standard (H.264, which I’ll focus on for this post) and many bits of hardware are able to accelerate decoding. So, the question is not whether the CPU can decode the data in real time, but can any other hardware in the device (likely the graphics hardware) handle it ? These machines have Intel HD 4000 graphics and, per my reading of the literature, they are capable of accelerating H.264 video decoding.

  Great, so the hardware supports accelerated decoding. So it’s a done deal, right ? Not quite…

  Operating System Support
  An application can’t do anything pertaining to hardware without permission from the operating system. So the next question is : Does Mac OS X allow an application to access accelerated video decoding hardware if it’s available ? This used to be a contentious matter (notably, Adobe Flash Player was unable to accelerate H.264 playback on Mac in the absence of such an API) but then Apple released an official API detailed in Technical Note TN2267.

  So, does this mean that video is magically accelerated ? Nope, we’re still not there yet…

  Application Support
  It’s great that all of these underlying pieces are in place, but if an individual application chooses to decode the video directly on the CPU, it’s all for naught. An application needs to query the facilities and direct data through the API if it wants to leverage the acceleration. Obviously, at this point it becomes a matter of “which application ?”

  My friend eventually opted to get the pricier of the desktop Mac Mini models and we ran some ad-hoc tests since I was curious how widespread the acceleration support is among Mac multimedia players. Here are some programs I wanted to test, playing 1080p H.264 :

  • Apple QuickTime Player
  • VLC
  • YouTube with Flash Player (any browser)
  • YouTube with Safari/HTML5
  • YouTube with Chrome/HTML5
  • YouTube with Firefox/HTML5
  • Netflix

  I didn’t take exhaustive notes but my impromptu tests revealed QuickTime Player was, far and away, the most performant player, occupying only around 5% of the CPU according to the Mac OS X System Profiler graph (which is likely largely spent on audio decoding).

  VLC consistently required 20-30% CPU, so it’s probably leveraging some acceleration facilities. I think that Flash Player and the various HTML5 elements performed similarly (their multi-process architectures can make such a trivial profiling test difficult).

  The outlier was Netflix running in Firefox via Microsoft’s Silverlight plugin. Of course, the inner workings of Netflix’s technology are opaque to outsiders and we don’t even know if it uses H.264. It may very well use Microsoft’s VC-1 which is not a capability provided by the Mac OS X acceleration API (it doesn’t look like the Intel HD 4000 chip can handle it either). I have never seen any data one way or another about how Netflix encodes video. However, I was able to see that Netflix required an enormous amount of CPU muscle on the Mac platform.

  Conclusion
  The foregoing is a slight simplification of the video playback pipeline. There are some other considerations, most notably how the video is displayed afterwards. To circle back around to the original question : Can the Mac Mini handle full HD video playback ? As my friend found, the meager Mac Mini can do an admirable job at playing full HD video without loading down the CPU.

• FFMPEG Speed drops and warnings

  31 juillet 2018, par leo_dragons

  I’ve been trying to stream from a BlackMagic DeckLink Mini Recorder to 4 different outputs using FFMPEG, but i get a huge delay let say more than 60 seconds of delay, it takes a long time to buffer on any player and when i check the terminal i get these warnings :

  [decklink @ 0x4655e40] Decklink input buffer overrun!

  I’ve also noticed that i have a very slow capture speed like 0.5x. Here’s the string i use, i’m currently running on CentOS 7.5 :

  ffmpeg -f decklink -i "DeckLink Mini Recorder" -y -pix_fmt yuv420p -vcodec h264 -preset ultrafast -tune zerolatency -b 900k -g 48 -framerate 30 -movflags +faststart -vf scale=1280:720 -bufsize 400k -maxrate 1200k -benchmark -f flv "rtmp ://10.0.0.172:1935/CAMARAS/live9" -vcodec h264 -preset ultrafast -tune zerolatency -b 700k -g 48 -framerate 30 -movflags +faststart -vf scale=854:480 -bufsize 400k -maxrate 1000k -benchmark -f flv "rtmp ://10.0.0.172:1935/CAMARAS/live10" -vcodec h264 -preset ultrafast -tune zerolatency -b 400k -g 48 -framerate 30 -movflags +faststart -vf scale=854:480 -bufsize 400k -maxrate 500k -benchmark -f flv "rtmp ://10.0.0.172:1935/CAMARAS/live11" -vcodec h264 -preset ultrafast -tune zerolatency -b 200k -g 48 -framerate 30 -movflags +faststart -vf scale=640:360 -bufsize 300k -maxrate 300k -benchmark -f flv "rtmp ://10.0.0.172:1935/CAMARAS/live12" > /dev/null 2>&1 &

  But if i run this string alone i get decent capture speed, but i still have an awful latency 30ish seconds :

  ffmpeg -f decklink -i "DeckLink Mini Recorder" -y -pix_fmt yuv420p -vcodec h264 -preset ultrafast -tune zerolatency -b 900k -g 48 -framerate 30 -movflags +faststart -vf scale=1280:720 -bufsize 400k -maxrate 1200k -benchmark -f flv "rtmp ://10.0.0.172:1935/CAMARAS/live9"

  Any help will be highly appreciated.

  Tahnk you.

• Révision 19769 : Report de r19768 :

  27 juillet 2012, par RastaPopoulos -

  Mini amélioration du dateur : pouvoir passer un pas au timepicker car 30min par défaut ça ne convient pas à un paquet de sites à mon avis (tous ceux que je connais qui utilisent Agenda râlent de pas pouvoir caler l’heure d’un événement plus précisément). Tout est pareil par défaut, mais au moins ça se (...)