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• ffmpeg avformat_open_input() failed to open a dshow device url containing Chinese Characters

  16 octobre 2024, par Sang

  The USB Webcam is OK, but the device I want to use is a "virtual camera" named "无他伴侣(竖屏)", whose video is from the smart phone like Android or iOS. Connect the phone to PC, run an app on the phone, then run a PC client application, which can preview the video. The phone app is called "无他相机", and the PC app is called "无他伴侣", its website is https://www.wuta-cam.com/.

  


  I run FFmpeg at the Windows Commandline with the command ffmpeg -list_devices true -f dshow -i dummy, it's OK to list the devices.(in order to display Chinese correctly, run chcp 65001 in advance.)

  


  Run the command ffplay -f dshow -i video="无他伴侣(竖屏)", it's OK to play the video.(of course you need to comfirm its PC client previewing fine in advance.)

  


  Now I want to get the decoded frames from that virtual camera in my program, I call avformat_open_input() with video=无他伴侣(竖屏), it failed, the return value is -5, I/O error.

  


  Anyone knows the reason ?

  


  Below is my code snippet.

  


  avdevice_register_all();
avcodec_register_all();
//const char * url= "video=Logitech Webcam C930e";// This is fine.
char url[] = "video=无他伴侣(竖屏)";// This is bad.

AVFormatContext *pFmtCtx = avformat_alloc_context();
AVInputFormat *iformat = av_find_input_format("dshow");
int nRet = 0;
nRet = avformat_open_input(&pFmtCtx, url, iformat, NULL);
if (nRet)
{
    const size_t buffer_size = 256;
    char err_description[buffer_size];
    av_strerror(nRet, err_description, buffer_size);
    printf("%s.\n", err_description);// --> I/O error.
    printf("FAILED to open input.(Line:%d,%d)\n",  __LINE__, nRet);
    return -1;
}


  


• ffmpeg : VLC won’t open .sdp files generated by ffmpeg

  8 mai 2020, par tiredamage42

  TLDR : VLC or Quicktime won’t open .sdp video stream files generated by ffmpeg, even though ffplay does.

  



  Web development and ffmpeg noob, so apologies if I’m using the wrong terminology :

  



  I’m trying to stream my desktop capture (on OSX) using ffmpeg, sending it out via rtp protocol. 
As of right now I’m just testing it out by streaming it over a port in my localhost (4000). And trying to play it locally.

  



  The problem is that when I try and open the .sdp file generated by the ffmpeg command, VLC opens it and immediately stops, no errors or anything, and shows that it has a duration of 0:00. Quicktime won’t event open the file in the first place.

  



  ffplay does play the stream and I can see my desktop in the player window (with a significant loss in quality though). Even so there are a ton of warning and errors that show up intermittently (outlined below)

  



  I’m not sure if it’s a problem in the way I start the ffmpeg stream, the command is after a ton of iterations of trying to just make it work, so my options might be way wrong.

  



  command to 'serve' the desktop capture :

  



  ./ffmpeg -f avfoundation -s 1920x1080 -r 60 -i "1" -an \
-vcodec libx264 -preset ultrafast -tune zerolatency -pix_fmt yuv420p \
-sdp_file video.sdp -rtsp_transport tcp -f rtp rtp://127.0.0.1:4000


  



  SDP file that’s generated with the ffmpeg command :

  



  SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 58.29.100
m=video 4000 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1


  



  ffplay command used to play the stream :

  



  ./ffplay -probesize 32 -analyzeduration 0 -sync ext \
-fflags nobuffer -fflags discardcorrupt -flags low_delay -framedrop \
-strict experimental -avioflags direct \
-protocol_whitelist file,rtp,udp -I video.sdp


  



  For a while before ffplay starts I see a bunch of these errors repeating (in red) :

  



  [h264 @ 0x7ff6b788de00] non-existing PPS 0 referenced
[h264 @ 0x7ff6b788de00] decode_slice_header error
[h264 @ 0x7ff6b788de00] no frame!


  



  then the window seems to 'catch up' to the stream and actually shows the desktop capture, and I get these errors and warnings on a regular interval :

  



  1- in a yellow warning color :

  



  [sdp @ 0x7fc85b830600] RTP: missed 4 packets
[sdp @ 0x7fc85b830600] max delay reached. need to consume packet


  



  2-in a red error color :

  



  [h264 @ 0x7fc85b02aa00] out of range intra chroma pred mode
[h264 @ 0x7fc85b02aa00] error while decoding MB 132 32


  



  (I have a feeling that the above errors have to do with previewing the desktop capture in the desktop I’m capturing and causing pixels in the display to overflow)

  



  Edit :
So, I solved the issue soon after posting, but will leave this up in case anyone runs into the same problem.

  



  The solution was to remove the top line in the .sdp file that said SDP:

  


• '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 !