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• 'arecord' works but FFMPEG 'cannot open audio device'

  16 mai 2020, par kwithnail

  On my Linux-based QNAP NAS, I can successfully record my Loopback audio device using :

  



  # arecord -D default:CARD=Loopback test.wav


  



  However, FFMPEG cannot use this same audio device. It returns :

  



      [alsa @ 0x5a45880] cannot open audio device hw:default:CARD=Loopback (No such file or directory)
hw:default:CARD=Loopback: Input/output error


  



  I've also tried any number of hw: options in FFMPEG. For what it's worth, the arecord -l command returns :

  



  **** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC262 Analog [ALC262 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Loopback [Loopback], device 1: Loopback PCM [Loopback PCM]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


  



  arecord -L returns :

  



  [~] # arecord -L
null
    Discard all samples (playback) or generate zero samples (capture)
sysdefault:CARD=PCH
    HDA Intel PCH, ALC262 Analog
    Default Audio Device
front:CARD=PCH,DEV=0
    HDA Intel PCH, ALC262 Analog
    Front speakers
sysdefault:CARD=Loopback
    Loopback, Loopback PCM
    Default Audio Device
front:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    Front speakers
surround21:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    4.0 Surround output to Front and Rear speakers
surround41:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Loopback,DEV=0
    Loopback, Loopback PCM
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers


  



  FFMPEG command and response is :

  



  [~] # /share/CACHEDEV1_DATA/.qpkg/ffmpeg/ffmpeg -f alsa -i hw:default:CARD=Loopback test.mp3
ffmpeg version 4.2.1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
ALSA lib ../../../src/pcm/pcm.c:2564:(snd_pcm_open_noupdate) Unknown PCM hw:default:CARD=Loopback
[alsa @ 0x5f64800] cannot open audio device hw:default:CARD=Loopback (No such file or directory)
hw:default:CARD=Loopback: Input/output error


  



  FFMPEG -sources alsa gives :

  



  [~] # /share/CACHEDEV1_DATA/.qpkg/ffmpeg/ffmpeg -sources alsa
ffmpeg version 4.2.1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Auto-detected sources for alsa:
ALSA lib ../../../src/control/control.c:1375:(snd_ctl_open_noupdate) Invalid CTL hw:0
Cannot list sources.


  



  Can anyone shed some light on why this is impossible in FFMPEG and suggest what I'm doing wrong here ? FFMPEG includes the ALSA module, and is version 4.2.1. Thanks !

  


• GNU GPL licensing - x264 encoder (H.264) [closed]

  2 septembre 2015, par Prof

  I’m a little lost here. I have a few questions and i’m just after yes/no answers with a a description as to how you arrived at the answer. I’ve done some searching, and I’ve seen GNU GPL questions asked many times, but I’ve struggled to find a clear answer to my last question.

  I’m on a commercial proprietary project, and I want to produce H.264 video using the free x264 encoder (http://www.videolan.org/developers/x264.html), which apparently is under the GNU GPL license (2.0 it seems).

  From my limited understanding, if I link the x264 libraries then I have to distribute my source code, even if I’m just making calls into it. Correct ?

  If the license was GNU lesser, then I wouldn’t have to do this ? Correct ?

  If I distribute x264.exe with my application (alongside it as a separate .exe), so my application calls it as a separate process, do I still need to distribute my source code ? I believe the answer is no, but I would have to distribute the x264 source code, correct ?

  Thanks

• Exporting MPEG Transport Stream (.ts) keyframes to images in C/C++ ? Libavcodec / FFMPEG ?

  11 mai 2021, par CyberBully2003

  I have some buffers made up of 188 byte TS packets. When I write them to a file, I can successfully view these .ts files in a video player. MPEG-2/H.264 is the format of the Transport Streams.

  


  Now, I would like to export the keyframes from these Transport Streams buffers (or .ts files) as .jpeg or some other common image format in my C/C++ project.

  


  This is a trivial task from the command line using ffmpeg, where I just feed it the .ts file and some parameters.

  


  However, for the purpose of this project, I would like to accomplish this conversion/exporting of keyframes as images code-side in my current C/C++ directory because the raw bytes from these generated images will be put into another format.

  


  People online seem to recommend using libavcodec. There is an mpegets file in the ffmpeg source that seems like it might have some of the backend to do what I want.

  


  However, the steps needed to achieve this task using the library is not apparent.

  


  I know I could call ffmpeg from C++ and use stdin, but this isn't a preferred solution for this project.

  


  If someone could give me some guidance (and even better some example code) to accomplish this task, it would be greatly appreciated !