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• Projecting camera feed with a delay

  28 septembre 2022, par Viktor Vošček

  I'm working on a project which involves capturing output from a camera via HDMI (Sony Alpha A7 IV), and projecting it via a laser/lamp projector, but the catch is that the stream which is going into the projector should be delayed by 4 minutes. (If you start recording something at 10:00am, it will start playing back at 10:04am, etc.) It should be capturing and playing back the feed non-stop for the whole day.

  


  First I was thinking of using FFplay to display a DirectShow stream from a HDMI capture card (like the Elgato 4K60 Pro) and opening the FFplay window on the 'projector screen', but I wasn't able to find any way to manually add delay to the stream. My second idea was to record the actual feed to a video file, and then immediately play it back in intervals (still using FFmpeg+FFplay).

  


  Any other ideas/thoughts ?

  


• configure : print_in_columns : Replace pr with awk

  27 avril 2019, par Alexander Strasser

  configure : print_in_columns : Replace pr with awk
  Get rid of pr dependency and write the columns strictly
  
  alphabetical without page size considerations (POSIX
  
  specifies 66 lines as default).
  Setting the page size via pr's -l option was considered,
  
  but as there is issue #5680 which wants to avoid pr
  
  mainly because it's not in busybox, we chose to replace
  
  pr instead.
  Before pr would attempt to write pages, thus if a page
  
  boundary was reached, the output looked confusing as one
  
  couldn't see there was a new page and the alphabetical
  
  order was disrupted when scanning down one of the columns.
  This change is based on a shell implementation submitted
  
  before by Yejun.
  Possible differences to the current version using pr :
  
  1. pr implementations should truncate items to not overflow columns ;
  
     depending on how it's done not truncating shall be better IMHO.
  
  2. pr implementations might balance columns differently ;
  
     we use minimum number of lines and might end up not
  
     using all columns or might have lesser entries in the
  
     last column(s)
  
  3. we use spaces only for padding the columns ; at least the GNU pr
  
     version on my system also by default stuffs in tabs in addition
  
     to a single space in between columns. I don't see that this
  
     behaviour is demanded by POSIX, though I might be very well
  
     overlooking things. Anyway for our use case I can't see a need
  
     for having the additional tabs, or why it would be better compared
  
     to padding with spaces only.
  Fixes output for sizes with width < column width, too.
  Fixes remaining part of ticket #5680
  Contributor : Guo, Yejun <yejun.guo@intel.com>
  

  • [DH] configure

• How can I capture simple video input with audio from a capture device

  17 décembre 2020, par Geoff Sweet

  I'm using ffmpeg on Arch linux and trying to convert some old video to digital. The setup is pretty straightforward and if I connect to the capture device with VLC I get the video and audio just fine. So now I want to capture that with ffmpeg and write it to a file so I can edit it and clean it up. I'm only so-so familiar with ffmpeg and I've been digging through the man pages and here is where I am at.

  


  This command captures perfect audio, but no video :

  


  ffmpeg -f alsa -ac 2 -i front:CARD=Capture,DEV=0 out.mpeg


  


  This command captures perfect video ;

  


  ffmpeg -f video4linux2 -i /dev/video0 out.mpeg


  


  captures the video signal great, but with no audio. So combining them together should give me :

  


  ffmpeg -y -f alsa -ac 2 -i front:CARD=Capture,DEV=0 -f video4linux2 -i /dev/video0 out.mpeg


  


  But that command kinda falls on it's face. I get the audio, but no video :

  


  ffmpeg -y -f alsa -ac 2 -i front:CARD=Capture,DEV=0 -f video4linux2 -i /dev/video0 out.mpeg
ffmpeg version n4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 10.2.0 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-amf --enable-avisynth --enable-cuda-llvm --enable-lto --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmfx --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librav1e --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-shared --enable-version3
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'front:CARD=Capture,DEV=0':
  Duration: N/A, start: 1608093176.894565, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
[video4linux2,v4l2 @ 0x56248fe0ab80] Dequeued v4l2 buffer contains corrupted data (0 bytes).
Input #1, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 0.000000, bitrate: 995328 kb/s
    Stream #1:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 1920x1080, 995328 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #1:0 -> #0:0 (rawvideo (native) -> mpeg1video (native))
  Stream #0:0 -> #0:1 (pcm_s16le (native) -> mp2 (native))
Press [q] to stop, [?] for help
[video4linux2,v4l2 @ 0x56248fe0ab80] Dequeued v4l2 buffer contains corrupted data (0 bytes).
    Last message repeated 30 times
[alsa @ 0x56248fdb3840] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[mpeg @ 0x56248fe0dfc0] VBV buffer size not set, using default size of 230KB
If you want the mpeg file to be compliant to some specification
Like DVD, VCD or others, make sure you set the correct buffer size
Output #0, mpeg, to 'out.mpeg':
  Metadata:
    encoder         : Lavf58.45.100
    Stream #0:0: Video: mpeg1video, yuv420p(progressive), 1920x1080, q=2-31, 200 kb/s, 30 fps, 90k tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.91.100 mpeg1video
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: N/A
    Stream #0:1: Audio: mp2, 48000 Hz, stereo, s16, 384 kb/s
    Metadata:
      encoder         : Lavc58.91.100 mp2
frame=    2 fps=0.0 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=2.0 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=1.3 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=1.0 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.8 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.7 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.6 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.5 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.4 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.4 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.4 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.3 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.3 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.3 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.3 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.2 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/sframe=    2 fps=0.1 q=3.2 size=       0kB time=01:48:49.26 bitrate=   0.0kbits/s[video4linux2,v4l2 @ 0x56248fe0ab80] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=0 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=2020 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=4061 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=6102 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=8143 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=10184 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=12225 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=14266 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=16307 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=18348 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=20389 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=22430 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=24471 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=26512 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=28553 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=30594 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=32635 size=36451
[mpeg @ 0x56248fe0dfc0] buffer underflow st=0 bufi=34676 size=36451
frame=    2 fps=0.1 q=2.0 Lsize=    1470kB time=01:48:49.30 bitrate=   1.8kbits/s speed= 221x    
video:63kB audio:1388kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.314351%
Exiting normally, received signal 2.


  


  what I would ideally like is just a fairly raw 2ch stereo "dump" of what comes through the capture card.

  


  As always, I super appreciate any advice