Sur d’autres sites (7246)

• The duration of movie file recorded by AVAssetWriter is not correct

  1er mars 2016, par ideawu

  I am recording video files with AVAssetWriter combining with AVCaptureVideoDataOutputSampleBufferDelegate. So I can take control over every frame the camara gives in the method :

  - (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
  
      double time = CMTimeGetSeconds(CMSampleBufferGetPresentationTimeStamp(sampleBuffer));
  
      NSLog(@"%f", time);
  
      [_videoInput appendSampleBuffer:sampleBuffer];
  
  }

  So I am so sure how many samples have been written to AVAssetWriter via AVAssetWriterInput, and I know exactly the start time and end time of the samples being written. The duration is calculated by end_time - start_time. Say the duration calculated in the video capture programm is 0.5 second.

  I get the .mov/.mp4 file on disk, inspected with ffmpeg -i, it shows a very different duration.

  ffmpeg -i m003.mp4 2>&1 | grep Dura
  
    Duration: 00:00:01.37, start: 0.836667, bitrate: 95 kb/s

  The movie file show a duration of 1.37 seconds, which it’s quite different with the EXACT duration 0.5.

  Does any one knows the reason ?

• avconv/ffmpeg command to encode nice full hd webm for chrome

  18 mars 2016, par xavier.seignard

  People from the artistic direction gave me big .mov and .mp4 that I need to put on a web app, but so far they are so huge that decoding/rendering is kinda bad on chrome (this is a chrome only experience since it will run on electron at the end).

  I’d like to re-encode them in .webm since it seems to have the best support in chrome.

  But I’m kinda lost on how to re-encode them without significative visual quality lost.

  For now I use (taken from https://trac.ffmpeg.org/wiki/Encode/VP8)

  ffmpeg -i myVid.mp4 -c:v libvpx -crf 8 -b:v 2M -c:a libvorbis myVid.webm

  So, does anyone have a nice avconv/ffmpeg command that will produce nice and easy to render .webm ?

  Regards.

• Encoding of two full hd streams in Linux + GPU with Intel HD4000 / VA API / FFMPEG / OpenGL

  30 juin 2016, par qknight

  i want to encode/stream two full hd streams in realtime from my laptop to a remote location using linux/xorg on the host.

  VA API

  for this i’ve been playing with the VA API but the performance is pretty bad with 5.59 fps (see paste below).

  FFMPEG

  using ffmpeg with CPU encoding i get about 200 fps but then all cores of my Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz are busy and the fan turns on.

  future plans

  i want GPU support in encoding and later integrate this into a program which streams a virtual xorg ’screen’, see https://lastlog.de/wiki/index.php/Raspberry_PI_virtual_screen for more details on my plans.

  maybe h264 isn’t even what i want ? so if someone advices towards a different implementation, i’d welcome that.

  besides VA API there seems to be QuickSync but i didn’t experiment with that yet as it is not packaged on NixOS just yet.

  note : i need a library to have a smooth integration into the code.

  h264encode -w 1920 -h 1080 —profile MPSource frame is 1920x1080 and will code clip to 1920x1088 with crop
  INPUT:Try to encode H264...
  
  INPUT : Resolution : 1920x1080, 60 frames
  
  INPUT : FrameRate : 30
  
  INPUT : Bitrate : 14929920
  
  INPUT : Slieces : 1
  
  INPUT : IntraPeriod : 30
  
  INPUT : IDRPeriod : 60
  
  INPUT : IpPeriod : 1
  
  INPUT : Initial QP : 26
  
  INPUT : Min QP : 0
  
  INPUT : Source YUV : AUTO generated
  
  INPUT : Coded Clip : /tmp/test.264
  
  INPUT : Rec   Clip : Not save reconstructed frame
  libva info : VA-API version 0.38.1
  
  libva info : va_getDriverName() returns 0
  
  libva info : Trying to open /run/opengl-driver/lib/dri/i965_drv_video.so
  
  libva info : Found init function __vaDriverInit_0_38
  
  libva info : va_openDriver() returns 0
  
  Use profile VAProfileH264Main
  
  Support rate control mode (0x12):CBR CQP 
  
  RateControl mode : CQP
  
  Support VAConfigAttribEncPackedHeaders
  
  Support packed sequence headers
  
  Support packed picture headers
  
  Support packed slice headers
  
  Support packed misc headers
  
  Support 1 RefPicList0 and 1 RefPicList1
  
  Loading data into surface 15.....Complete surface loading
  
        \00000059(054456 bytes coded)
  PERFORMANCE :   Frame Rate : 5.59 fps (60 frames, 10730 ms (178.83 ms per frame))
  
  PERFORMANCE :   Compression ratio : 51:1
  
  PERFORMANCE :     UploadPicture : 10467 ms (174.45, 97.55% percent)
  
  PERFORMANCE :     vaBeginPicture : 0 ms (0.00, 0.00% percent)
  
  PERFORMANCE :     vaRenderHeader : 1 ms (0.02, 0.01% percent)
  
  PERFORMANCE :     vaEndPicture : 42 ms (0.70, 0.39% percent)
  
  PERFORMANCE :     vaSyncSurface : 244 ms (4.07, 2.27% percent)
  
  PERFORMANCE :     SavePicture : 7 ms (0.12, 0.07% percent)
  
  PERFORMANCE :     Others : -31 ms (71582787.75, 40027653.91% percent)
  
  (Multithread enabled, the timing is only for reference)
  

  i’ve seen https://www.reddit.com/r/linux/comments/1qk1yu/is_there_currently_opensource_software_to_encode/ though but i’m not sure what do do with it.