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• Can you think of a reason why windows might not enable audio if noone is logged in ?

  3 juillet 2017, par Caius Jard

  I’m having a bizarre problem with some virtual servers created to record podcasts. They run on amazon AWS as windows server 2012 instances and a small c# app tells FFMPEG to do the heavy lifting of capturing from the virtual screen and reading from the virtual sound card (Virtual Audio Cable : https://en.wikipedia.org/wiki/Virtual_Audio_Cable) via DirectShow filters

  The problem I have is if I leave the machine to do its stuff unattended, the recordings are sometimes silent. If I log in via VNC and watch it doing its stuff the audio is recorded just fine. All other aspects of the test op are the same, and the virtual machine is shut down between successive recordings so each one should theoretically be a clean slate. The app runs under a logged in session (hence the use of VNC rather than RDP)

  I’m now wondering if there is some optimisation of the windows sound engine whereby it doesn’t bother playing audio if it thinks noone is listening. The confusing thing to me is that not every virtual machine suffers these problems ; some of them record fine (and they’re all created from the same seed virtual hard disk image) in unattended mode

  I’m asking this question with the aim of getting together a list of things I can check/look into/debug.. I don’t have much knowledge of how MME/DirectSound/WASAPI work internally...

• Converting FFMpeg Video to android playable video

  15 avril 2021, par Soham Samanta

  I had some image sequence and I used them to make a video using FFMpeg. It palyed well on VLC (windows and android) but not on built in android video player.
Codec and container info of the video is the following -

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '../clg/clg_eq_final_injected.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.83.100
  Duration: 00:00:12.13, start: 0.000000, bitrate: 9058 kb/s
    Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 4096x2048, 9057 kb/s, 24 fps, 24 tbr, 12288 tbn, 24576 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Side data:
      spherical: equirectangular (0.000000/0.000000/0.000000)


  


  I made a workaround by uploading the video on youtube. Then I downloaded it again. It's codec info is following -

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '../clg/clg_eq_test.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2020-05-17T08:06:01.000000Z
  Duration: 00:00:12.14, start: 0.000000, bitrate: 738 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 607 kb/s, 24 fps, 24 tbr, 12288 tbn, 48 tbc (default)
    Metadata:
      creation_time   : 2020-05-17T08:06:01.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 05/17/2020.
    Side data:
      stereo3d: 2D
      spherical: equirectangular (0.000000/0.000000/0.000000)
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      creation_time   : 2020-05-17T08:06:01.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 05/17/2020.


  


  I noticed that the first video does not have any audio stream (since it's just an image sequence). But youtube arbitrarily added an audio stream. (I tried on android after adding an audio stream with it but no luck)
What I know -

  


  

  1. Android does not natively support motion JPEG.

  


  2. H264 is supported by android.

  


  


  Q1. What is the difference between h264(constrained baseline) vs h264(main) ?
Q2. Why the first video is not natively supported on android ?
My uploaded youtube video is here.

  


  Ref :

  


  Conversion from mjpeg to mp4 (libx264) with FFmpeg

  


  convert format from yuvj420p to yuv420p

  


  How to create a video from images with FFmpeg ?

  


• kmsgrab : Use GetFB2 if available

  5 juillet 2020, par Mark Thompson

  kmsgrab : Use GetFB2 if available
  The most useful feature here is the ability to automatically extract the
  
  framebuffer format and modifiers.  It also makes support for multi-plane
  
  framebuffers possible, though none are added to the format table in this
  
  patch.
  This requires libdrm 2.4.101 (from April 2020) to build, so it includes a
  
  configure check to allow compatibility with existing distributions.  Even
  
  with libdrm support, it still won't do anything at runtime if you are
  
  running Linux < 5.7 (before June 2020).
  

  • [DH] configure
  • [DH] libavdevice/kmsgrab.c