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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 produces mp4 I cannot load on latest Safari on iOS

  28 mars 2016, par Michael Heuberger

  When I encode a video with these ffmpeg parameters (based on images), I cannot play that mp4 it produces on latest Safari (inside a tag) inside my iPhone 6s using the latest iOS too :

  ffmpeg 
  
  -r 15.279071668502123 
  
  -f image2 -thread_queue_size 64 
  
  -i /home/michael-heuberger/abcd/frames/%d.webp 
  
  -y 
  
  -an 
  
  -vcodec libx264 
  
  -vf scale=trunc(iw/2)*2:trunc(ih/2)*2 
  
  -crf 16 
  
  -preset fast 
  
  -profile:v baseline 
  
  -pix_fmt yuv420p 
  
  -loglevel warning 
  
  -movflags faststart 
  
  /home/michael-heuberger/abcd/videomail_good.mp4 

  I think the above parameters should be solid. I am adding baseline and yuv420p, yet no luck on Safari 9. Why ?

  This makes it difficult for me to play videomails recorded on www.videomail.io on iOS devices.

  Am I missing something here ? Already did lots of research and tried various combinations, no luck.

  If you want to reproduce that, easy : just record a video on www.videomail.io and after that, copy the link of the recorded video page to your iPhone or just download it for local investigation.

  Any clues very welcome !

• Can I record a video without using UIImagePickerController ?

  24 mai 2016, par SUKIYAKI

  Can I record a video without using UIImagePickerController ?
  Of course without needing to jailbreak or anything else that would cause the App Store to reject the app.

  I think there is a way to access video device not using UIImagePickerController because these camera applications can record video and work on iPhone 2G/3G which utilizes ffmpeg :

  • iVideoCamera
  • iVidCam

  I pick this code up by googling.

  AVFormatParameters formatParams;
  
  AVInputFormat *iformat;
  
  
  
  formatParams.device = "/dev/video0";
  
  formatParams.channel = 0;
  
  formatParams.standard = "ntsc";
  
  formatParams.width = 640;
  
  formatParams.height = 480;
  
  formatParams.frame_rate = 29;
  
  formatParams.frame_rate_base = 1;
  
  filename = "";
  
  iformat = av_find_input_format("video4linux");
  
  
  
  av_open_input_file(&ffmpegFormatContext,
  
                   filename, iformat, 0, &formatParams);

  This code tell me how to open camera device, but I don’t know device path of iPhone.

  How do iVideoCamera and iVidCam record video ?