Recherche avancée

Sur d’autres sites (10712)

• v4l2loopback+ffmpeg input for uvc gadget

  13 mai, par Mosi

  I'm trying to use an MP4 video file as the input for a UVC Gadget setup on my Raspberry Pi 4 Model B, but I'm running into an issue when streaming through V4L2.

  


  Goal :

  


  To emulate a webcam that streams a looping MP4 video file to a Windows 11 host.

  


  My setup :

  


  

  • Hardware : Raspberry Pi 4 Model B

  


  • OS : Raspberry Pi OS Lite 64-bit (2025-05-06-raspios-bookworm-arm64-lite)

  


  • Kernel : 6.12.25+rpt-rpi-v8

  


  • Host System : Windows 11

  


  • UVC Gadget version : v0.3.0

  


  


  Workflow :

  


  [MP4 Video] → [FFmpeg] → [V4L2 Loopback] → [UVC Gadget] → Windows sees virtual webcam


  


  What works :

  


  The UVC Gadget works perfectly when I use a real webcam as the source (e.g., /dev/video0). Windows detects the virtual webcam and displays a smooth video stream.

  


  The problem :

  


  When I try to use an MP4 video file through FFmpeg and send it to the loopback device (/dev/video3), the UVC Gadget fails with the following error :

  


  ---

  


  Command I'm using :

  


  ffmpeg -re -stream_loop -1 -i input.mp4 -vf scale=640:480 \
  -c:v rawvideo -pix_fmt yuyv422 -r 30 -f v4l2 /dev/video3


  


  Then I run :

  


  sudo uvc-gadget -d /dev/video3 uvc.0


  


  Output :

  


  bRequestType 21 bRequest 01 wValue 0200 wIndex 0001 wLength 0022
streaming request (req SET_CUR cs 02)
setting commit control, length = 34
Setting format to 0x56595559 640x480
=== Setting frame rate to 30 fps
Starting video stream.
--> [At this point I open the camera on the Windows host]
/dev/video3: 2 buffers requested.
Failed to export buffer 0.
Failed to export buffers on source: Inappropriate ioctl for device (25)


  


  ---

  


  Things I've tried :

  


  

  • Multiple FFmpeg formats, resolutions, and pixel formats

  


  • Various ffmpeg buffer and framerate tweaks

  


  • Different UVC Gadget versions

  


  • GitHub related projects (showcamera, etc.)

  


  • Older Raspberry Pi OS versions

  


  


  Most guides and GitHub projects I found are outdated (5+ years old), and newer methods seem undocumented or incompatible with current kernel/UVC gadget tools.

  


  ---

  


  My question :

  


  How can I stream an MP4 file as a virtual webcam using UVC Gadget without getting ioctl errors ?
  
Is there a proper way to set up FFmpeg and loopback devices so that UVC Gadget can read the stream correctly ?

  


  Any modern working example or tips would be very appreciated. Thanks in advance !

  


• How to quote a file name with a single quote in ffmpeg movie= filter notation ? [closed]

  26 mai, par PieterV

  I am trying to run ffmpeg using a file that contains a single quote ' in the filename.

  


  I tried to follow the docs that say I should replace a ' with '\''.
  
And a ticket that says I should replace a ' with \\\\\'.

  


  I've tried both, and can't get get it working.

  


  E.g. docs format :

  


  ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D\:\\Test\\Interlaced - Dragons'\'' Den - S14E02 - Episode 2.mkv'[out0+subcc]" -show_packets -print_format json

{
[Parsed_movie_0 @ 00000222a2f82200] Failed to avformat_open_input 'D:\Test\Interlaced - Dragons Den - S14E02 - Episode 2.mkv'
[AVFilterGraph @ 00000222a2f76ec0] Error processing filtergraph: No such file or directory
movie='D\:\\Test\\Interlaced - Dragons'\'' Den - S14E02 - Episode 2.mkv'[out0+subcc]: No such file or directory


  


  E.g. ticket format :

  


  ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D\:\\Test\\Interlaced - Dragons\\\\\' Den - S14E02 - Episode 2.mkv'[out0+subcc]" -show_packets -print_format json

{
[Parsed_movie_0 @ 00000158613d2080] Failed to avformat_open_input 'D:\Test\Interlaced - Dragons\\ Den - S14E02 - Episode 2.mkv[out0+subcc]'
[AVFilterGraph @ 00000158613c6ec0] Error processing filtergraph: No such file or directory
movie='D\:\\Test\\Interlaced - Dragons\\\\\' Den - S14E02 - Episode 2.mkv'[out0+subcc]: No such file or directory


  


  > dir "D:\Test\Interlaced - Dragons' Den - S14E02 - Episode 2.mkv"

    Directory: D:\Test

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---           4/20/2025 11:38 AM       18059051 Interlaced - Dragons' Den - S14E02 - Episode 2.mkv


  


  This is on Win11 using FFmpeg7.
  
Any ideas ?

  


  [Update]
  
I found a doc on escape filtergraph strings, did not help, I tried 0 to 7 \.

  


  I also found and tried the ffescape utility, the output it produces just uses a single \' and does not work.

  


  > echo "D:\Test\Interlaced - Dragons' Den - S14E02 - Episode 2.mkv" | ./ffescape.exe
=> D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\

> ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\'[out0+subcc]" -show_packets -print_format json
{
[Parsed_movie_0 @ 0000021348f12200] Failed to avformat_open_input 'D'
[AVFilterGraph @ 0000021348f06ec0] Error processing filtergraph: No such file or directory
movie='D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\'[out0+subcc]: No such file or directory


  


  [Update]
  
I found docs for ffmpeg filter script where I can place commands in a file.

  


  I tried ./ffprobe -loglevel error -read_intervals %00:01 -select_streams s:0 -f lavfi -/i "d:\filtergraph.txt" -show_packets -print_format json, and it load the script.

  


  Works : movie=test.mkv[out0+subcc]\ if test.mkv is in ffprobe dir.
Works : movie=test\'.mkv[out0+subcc]\ if test'.mkv is in ffprobe dir.
  
Not : movie=D:\test.mkv[out0+subcc]
  
Not : movie=D\:\\test.mkv[out0+subcc]
  
Not : movie=test space.mkv[out0+subcc]
  
Not : movie='test space.mkv[out0+subcc]'
  
Not : movie="test space.mkv[out0+subcc]"
  
Not : 'movie=test space.mkv[out0+subcc]'
  
Not : "movie=test space.mkv[out0+subcc]"

  


   :(

  


  Update with working answer

  


• How to dump ALL metadata from a media file, including cover image title ? [closed]

  9 avril, par Unideal

  I have an MP3 song :

  


  # ffprobe -hide_banner -i filename.mp3
Input #0, mp3, from 'filename.mp3':
  Metadata:
    composer        : Music Author
    title           : Song Name
    artist          : Singer
    encoder         : Lavf61.7.100
    genre           : Rock
    date            : 2025
  Duration: 00:03:14.04, start: 0.023021, bitrate: 208 kb/s
  Stream #0:0: Audio: mp3 (mp3float), 48000 Hz, stereo, fltp, 192 kb/s
      Metadata:
        encoder         : Lavc61.19
  Stream #0:1: Video: png, rgb24(pc, gbr/unknown/unknown), 600x600 [SAR 1:1 DAR 1:1], 90k tbr, 90k tbn (attached pic)
      Metadata:
        title           : Cover
        comment         : Cover (front)


  


  The task is to save its metadata to a text file and restore from that file later. Both goals should be accomplished with ffmpeg.

  


  The simpliest method is to run :

  


  # ffmpeg -i filename.mp3 -f ffmetadata metadata.txt


  


  After that, metadata.txt contains :

  


  ;FFMETADATA1
composer=Music Author
title=Song Name
artist=Singer
date=2025
genre=Rock
encoder=Lavf61.7.100


  


  I got global metadata only, but stream-specific info (cover image title and comment in my case) are missing.

  


  Google suggested a more complex form of the command above to extract all metadata fields without any exclusions :

  


  # ffmpeg -y -i filename.mp3 -c copy -map_metadata 0 -map_metadata:s:v 0:s:v -map_metadata:s:a 0:s:a -f ffmetadata metadata.txt


  


  But the output is exactly the same :

  


  ;FFMETADATA1
composer=Music Author
title=Song Name
artist=Singer
date=2025
genre=Rock
encoder=Lavf61.7.100


  


  Again, no info about the attached image.

  


  Please explain what am I doing wrong.