v4l2 encoder ignores input_format specification

[leezu]

Summary of the bug: With a video capture device providing both compressed Motion-JPEG and uncompressed YUYV, ffmpeg always chooses YUYV even if MJPEG is requested.

How to reproduce:

% ~/Downloads/ffmpeg -v 9 -loglevel 99 -i /dev/video0 -input_format mjpeg
ffmpeg version N-107804-gaa9eabb7a5-https://www.martin-riedl.de Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)                                   
  configuration: --prefix=/home/ffmpegBuild/out --enable-gpl --pkg-config-flags=--static --extra-version='https://www.martin-riedl.de' --ena
ble-gray --enable-libxml2 --enable-libfreetype --enable-fontconfig --enable-libbluray --enable-libass --enable-libaom --enable-libopenh264 -
-enable-libsvtav1 --enable-libvpx --enable-libx264 --enable-libx265 --enable-libmp3lame --enable-libopus --enable-libvorbis                 
  libavutil      57. 33.101 / 57. 33.101                                                                                                    
  libavcodec     59. 42.101 / 59. 42.101                                                                                                    
  libavformat    59. 30.100 / 59. 30.100                                                                                                    
  libavdevice    59.  8.101 / 59.  8.101                                                                                                    
  libavfilter     8. 46.103 /  8. 46.103                                                                                                    
  libswscale      6.  8.102 /  6.  8.102                                                                                                    
  libswresample   4.  8.100 /  4.  8.100                                                                                                    
  libpostproc    56.  7.100 / 56.  7.100                                                                                                    
Splitting the commandline.                                            
Reading option '-v' ... matched as option 'v' (set logging level) with argument '9'.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument '99'.
Reading option '-i' ... matched as input url with argument '/dev/video0'.                                                                   
Reading option '-input_format' ... matched as AVOption 'input_format' with argument 'mjpeg'.
Trailing option(s) found in the command: may be ignored.                                                                                    
Finished splitting the commandline.                                                                                                         
Parsing a group of options: global .                                                                                                        
Applying option v (set logging level) with argument 9.                                                                                      
Successfully parsed a group of options.                                                                                                     
Parsing a group of options: input url /dev/video0.                                                                                          
Successfully parsed a group of options.                                                                                                     
Opening an input file: /dev/video0.                                                                                                         
Probing video4linux2,v4l2 score:99 size:0                                                                                                   
[video4linux2,v4l2 @ 0x5d5a711060] fd:3 capabilities:84a00001                                                                               
[video4linux2,v4l2 @ 0x5d5a711060] Current input_channel: 0, input_name: Camera 1, input_std: 0
[video4linux2,v4l2 @ 0x5d5a711060] Querying the device for the current frame size
[video4linux2,v4l2 @ 0x5d5a711060] Setting frame size to 1280x720                                                                           
[video4linux2,v4l2 @ 0x5d5a711060] The V4L2 driver changed the pixel format from 0x32315559 to 0x47504A4D
[video4linux2,v4l2 @ 0x5d5a711060] Trying to set codec:rawvideo pix_fmt:yuv420p                                                             
[video4linux2,v4l2 @ 0x5d5a711060] The V4L2 driver changed the pixel format from 0x32315559 to 0x47504A4D
[video4linux2,v4l2 @ 0x5d5a711060] Trying to set codec:rawvideo pix_fmt:yuv420p                                                             
[video4linux2,v4l2 @ 0x5d5a711060] The V4L2 driver changed the pixel format from 0x32315659 to 0x47504A4D
[video4linux2,v4l2 @ 0x5d5a711060] Trying to set codec:rawvideo pix_fmt:yuv422p                                                             
[video4linux2,v4l2 @ 0x5d5a711060] The V4L2 driver changed the pixel format from 0x50323234 to 0x47504A4D
[video4linux2,v4l2 @ 0x5d5a711060] Trying to set codec:rawvideo pix_fmt:yuyv422                                                             
[video4linux2,v4l2 @ 0x5d5a711060] All info found                                                                                           
[video4linux2,v4l2 @ 0x5d5a711060] stream 0: start_time: 639.743 duration: NOPTS                                                            
[video4linux2,v4l2 @ 0x5d5a711060] format: start_time: 639.743 duration: NOPTS (estimate from bit rate) bitrate=147456 kb/s
Input #0, video4linux2,v4l2, from '/dev/video0':                                                                                            
  Duration: N/A, start: 639.742977, bitrate: 147456 kb/s                                                                                    
  Stream #0:0, 1, 1/1000000: Video: rawvideo, 1 reference frame (YUY2 / 0x32595559), yuyv422, 1280x720, 0/1, 147456 kb/s, 10 fps, 10 tbr, 10
00k tbn

Note that ffmpeg -list_formats all does list the mjpeg:

% ffmpeg -f video4linux2 -list_formats all -i /dev/video0
ffmpeg version 5.1-2+b1 Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 12 (Debian 12.1.0-7)
  configuration: --prefix=/usr --extra-version=2+b1 --toolchain=hardened --libdir=/usr/lib/aarch64-linux-gnu --incdir=/usr/include/aarch64-linux-gnu --arch=arm64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libglslang --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librist --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --disable-sndio --enable-pocketsphinx --enable-librsvg --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libplacebo --enable-libx264 --enable-shared
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  libavdevice    59.  7.100 / 59.  7.100
  libavfilter     8. 44.100 /  8. 44.100
  libswscale      6.  7.100 /  6.  7.100
  libswresample   4.  7.100 /  4.  7.100
  libpostproc    56.  6.100 / 56.  6.100
[video4linux2,v4l2 @ 0x5694e62800] Compressed:       mjpeg :          Motion-JPEG : 1280x720 320x240 640x360 640x480
[video4linux2,v4l2 @ 0x5694e62800] Raw       :     yuyv422 :           YUYV 4:2:2 : 1280x720 320x240 640x360 640x480
/dev/video0: Immediate exit requested

v4l2-ctl provides further details on supported fps

% v4l2-ctl --list-formats-ext --device /dev/video0
ioctl: VIDIOC_ENUM_FMT
        Type: Video Capture

        [0]: 'MJPG' (Motion-JPEG, compressed)
                Size: Discrete 1280x720
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 320x240
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 640x360
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 640x480
                        Interval: Discrete 0.033s (30.000 fps)
        [1]: 'YUYV' (YUYV 4:2:2)
                Size: Discrete 1280x720
                        Interval: Discrete 0.100s (10.000 fps)
                Size: Discrete 320x240
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 640x360
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 640x480
                        Interval: Discrete 0.033s (30.000 fps)

This bug was observed on a Snapdragon 7c arm64 based system with the Adreno 618 GPU.

[Balling]

Motion-JPEG and uncompressed YUYV, 

First of all, MJPEG is lossy. Without c copy there will be genration loss. Second of all, YUYV is 422, not 420, but MJPEG supports 422.

So I think it is all good.

[leezu]

yuyv422 at 1280x720 here only provides 10 fps (see the v4l2-ctl output above), whereas Motion-JPEG provides 30 fps.

So I think it is all good.

How do you suggest to capture 1280x720 resolution video at 30 fps with ffmpeg on this hardware? I assume the lossy MJPEG at 1280x720 will still be better than 640x360 YUYV. Even with -input_format mjpeg -c copy, yuyv422 is used.