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• ffmpeg doesn't seem to be working with multiple audio streams correctly

  21 juin 2017, par Caius Jard

  I’m having an issue with ffmpeg 3.2.2 ; ordinarily I ask it to make an MP4 video file with 2 audio streams. The command line looks like this :

  ffmpeg.exe
  
  -rtbufsize 256M 
  
  -f dshow -i video="screen-capture-recorder" -thread_queue_size 512 
  
  -f dshow -i audio="Line 2 (Virtual Audio Cable)" 
  
  -f dshow -i audio="Line 3 (Virtual Audio Cable)" 
  
  -map 0:v -map 1:a -map 2:a 
  
  -af silencedetect=n=-50dB:d=60 -pix_fmt yuv420p -y "c:\temp\2channelvideo.mp4"

  I’ve wrapped it for legibility. This once worked fine, but something is wrong lately - it doesnt seem to record any audio, even though I can use other tools like Audacity to record audio from these devices just fine

  I’m trying to do some diag on it by dropping the video component and asking ffmpeg to record the two audio devices to two separate files :

  ffmpeg.exe
  
  -f dshow -i audio="Line 2 (Virtual Audio Cable)" "c:\temp\line2.mp3" 
  
  -f dshow -i audio="Line 3 (Virtual Audio Cable)" "c:\temp\line3.mp3"

  ffmpeg’s console output looks like :

  Guessed Channel Layout for Input Stream #0.0 : stereo
  
  Input #0, dshow, from 'audio=Line 2 (Virtual Audio Cable)':
  
    Duration: N/A, start: 5935.810000, bitrate: 1411 kb/s
  
      Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
  
  Guessed Channel Layout for Input Stream #1.0 : stereo
  
  Input #1, dshow, from 'audio=Line 3 (Virtual Audio Cable)':
  
    Duration: N/A, start: 5936.329000, bitrate: 1411 kb/s
  
      Stream #1:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
  
  Output #0, mp3, to 'c:\temp\line2.mp3':
  
    Metadata:
  
      TSSE            : Lavf57.56.100
  
      Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, s16p
  
      Metadata:
  
        encoder         : Lavc57.64.101 libmp3lame
  
  Output #1, mp3, to 'c:\temp\line3.mp3':
  
    Metadata:
  
      TSSE            : Lavf57.56.100
  
      Stream #1:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, s16p
  
      Metadata:
  
        encoder         : Lavc57.64.101 libmp3lame
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
  
    Stream #0:0 -> #1:0 (pcm_s16le (native) -> mp3 (libmp3lame))
  
  Press [q] to stop, [?] for help

  The problem i’m currently having is that the produced mp3 are identical copies of line 2 only ; line 3 audio is not recorded. The last line is of concern ; it seems to be saying that stream 0 is being mapped to both output 0 and 1 ? Do I need a map command for each file also ? I thought it would be implicit due to the way i specified the arguments

• 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...

• How do I upscale an iOS App Preview video to 1080 x 1920 ? [closed]

  12 avril 2024, par Benjamin Thiel

  I just captured a video of my new app running on an iPhone 6 using QuickTime Player and a Lightning cable. Afterwards I created an App Preview project in iMovie, exported it and could successfully upload it to iTunes Connect.

  



  Apple requires developers to upload App Previews in different resolutions dependent on screen size, namely :

  



  

  • iPhone 5(S) : 1080 x 1920 or 640 x 1136

  


  • iPhone 6 : 750 x 1334 (what I have)

  


  • iPhone 6+ : 1080 x 1920

  


  



  Obviously, 1080 x 1920 is killing two birds with one stone. I know that upscaling isn't the perfect solution, but it's meeting my needs. Since I don't own a 6+, another recording session won't do the trick.

  



  Unfortunately, iTunes Connect is extremely picky about what to accept. Here's what I tried, to no avail :

  



  

  • Handbrake, iMovie, QuickTime do not support upscaling

  


  • MPEG Streamclip

  


  • ffmpeg -i input.mp4 -acodec copy -vf scale=1080:1920 output.mp4

  


  



  Strangely enough, iTunes Connect keeps complaining about the wrong resolution when I try to upload the output.mp4 of ffmpeg.