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• ffmpeg : join + crossfade 5 input files (video+audio) into one output file

  7 avril 2020, par Fab Sanchez

  I have 5 mp4 input videos (audio+video) that I want to 'join' into a single output video with a crossfade effect in between each pair of videos.
I want to 'crossfade' both the audio and the video, with a transition of 0.4s.
(Not an actual crossfade, more like video-2 fades in over video-1, video-1 does not need to fade out, but this is not the problem)

  



  I'm using ffmpeg-4.1.3-win64-static

  



  I have followed many tutorials and answers from here, but there are so many different ways to do it...

  



  Each one of the 5 videos is 1.024s long, duration obtained with ffprobe

  



  ffprobe.exe -i "0.mp4" -show_entries format=duration -v quiet -of csv="p=0"


  



  This is the command for both audio and video :
(I've reformatted the command so it is easier to read, it is issued as a single line in the command prompt)

  



  ffmpeg.exe -y -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4" 
-filter_complex "
[0:v]setpts=PTS-STARTPTS[v1];
[1:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(0.6/TB)[v2];
[2:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.2/TB)[v3];
[3:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.8/TB)[v4];
[4:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(2.4/TB)[v5];
[v1][v2]overlay[u1];[u1][v3]overlay[u2];[u2][v4]overlay[u3];[u3][v5]overlay,format=yuv420p[v];
[0][1]acrossfade=d=0.4[a0];
[a0][2]acrossfade=d=0.4[a1];
[a1][3]acrossfade=d=0.4[a2];
[a2][4]acrossfade=d=0.4[a]
" -map [v] -map [a] "output.mp4"


  



  When I do both audio and video into a single output file, output.mp4 can not be played on VLC, this is the vlc log :

  



  main debug: `file:///C:/project/input-videos/output.mp4' gives access `file' demux `any' path `/C:project/input-videos/output.mp4'
main debug: creating demux: access='file' demux='any' location='/C:/project/input-videos/output.mp4' file='C:\project\input-videos\output.mp4'
main debug: looking for access_demux module matching "file": 15 candidates
main debug: no access_demux modules matched
main debug: creating access: file:///C:/project/input-videos/output.mp4
main debug:  (path: C:\project\input-videos\output.mp4)
main debug: looking for access module matching "file": 26 candidates
main debug: using access module "filesystem"
main debug: looking for stream_filter module matching "prefetch,cache_read": 24 candidates
cache_read debug: Using stream method for AStream*
cache_read debug: starting pre-buffering
cache_read error: cannot pre fill buffer
main debug: looking for meta fetcher module matching "any": 1 candidates
main debug: no stream_filter modules matched
main warning: cannot insert stream filter prefetch,cache_read
main debug: looking for stream_filter module matching "any": 24 candidates
playlist debug: not enough data
...


  



  This is the output from ffmpeg :

  



  ffmpeg version 4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.3.1 (GCC) 20190414
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '0.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    location-eng    : +52.6899-001.8293/
    location        : +52.6899-001.8293/
  Duration: 00:00:01.02, start: 0.000000, bitrate: 13821 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 14002 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandle
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      handler_name    : SoundHandle
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    location-eng    : +53.4256-001.3580/
    location        : +53.4256-001.3580/
  Duration: 00:00:01.02, start: 0.000000, bitrate: 7094 kb/s
    Stream #1:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 7113 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandle
    Stream #1:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      handler_name    : SoundHandle
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from '2.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    location-eng    : +53.3927-001.5044/
    location        : +53.3927-001.5044/
  Duration: 00:00:01.02, start: 0.000000, bitrate: 7367 kb/s
    Stream #2:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 7394 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandle
    Stream #2:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 126 kb/s (default)
    Metadata:
      handler_name    : SoundHandle
Input #3, mov,mp4,m4a,3gp,3g2,mj2, from '3.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    location-eng    : +53.3927-001.5044/
    location        : +53.3927-001.5044/
  Duration: 00:00:01.02, start: 0.000000, bitrate: 8145 kb/s
    Stream #3:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 8192 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandle
    Stream #3:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      handler_name    : SoundHandle
Input #4, mov,mp4,m4a,3gp,3g2,mj2, from '4.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    location-eng    : +53.3927-001.5044/
    location        : +53.3927-001.5044/
  Duration: 00:00:01.02, start: 0.000000, bitrate: 6241 kb/s
    Stream #4:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 6241 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandle
    Stream #4:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 126 kb/s (default)
    Metadata:
      handler_name    : SoundHandle
Stream mapping:
  Stream #0:0 (h264) -> setpts
  Stream #0:1 (aac) -> acrossfade:crossfade0
  Stream #1:0 (h264) -> format
  Stream #1:1 (aac) -> acrossfade:crossfade1
  Stream #2:0 (h264) -> format
  Stream #2:1 (aac) -> acrossfade:crossfade1
  Stream #3:0 (h264) -> format
  Stream #3:1 (aac) -> acrossfade:crossfade1
  Stream #4:0 (h264) -> format
  Stream #4:1 (aac) -> acrossfade:crossfade1
  format -> Stream #0:0 (libx264)
  acrossfade -> Stream #0:1 (aac)
  Press [q] to stop, [?] for help


  



  When I do the video only it is fine. The duration of the output.mp4 file generated for video-only is 3.4s

  



  When I do the audio only it is also fine. The duration of the output.mp4 file generated for audio-only is 3.435s

  



  This is the command for video only :

  



  ffmpeg.exe -y  -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4" 
-filter_complex "
[0:v]setpts=PTS-STARTPTS[v1];
[1:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(0.6/TB)[v2];
[2:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.2/TB)[v3];
[3:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.8/TB)[v4];
[4:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(2.4/TB)[v5];
[v1][v2]overlay[u1];[u1][v3]overlay[u2];[u2][v4]overlay[u3];[u3][v5]overlay,format=yuv420p[v]
" -map [v] "output.mp4"


  



  This is the command for audio only :

  



  ffmpeg.exe -y  -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4" 
-filter_complex "
[0][1]acrossfade=d=0.4[a0];
[a0][2]acrossfade=d=0.4[a1];
[a1][3]acrossfade=d=0.4[a2];
[a2][4]acrossfade=d=0.4[a]
" -map [a] "output.mp4"


  



  What am I missing in order to generate one output file with both audio and video content ?

  



  Edit : Here's the full ffmpeg command + result for audio and video combined with "-loglevel debug" added. (Too big to add directly here, so I've added it to Pastebin)
https://pastebin.com/NLBc7Abb

  



  Work Around
Not a solution, but I found a work around :

  



  

  • Create video only output using command above, output to video.mp4

  


  • Create audio only output using command above, output to audio.mp4

  


  • Merge both video.mp4 and audio.mp4 into output.mp4 using the following command :

  


  



  ffmpeg.exe -y -i "video.mp4" -i "audio.mp4" -c:v copy -c:a aac output.mp4


  



  If anyone has any ideas as to why the combined audio+video command does not work, please let me know. :)

  


• 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 !

  


• Revert "lavf/id3v2dec : support multiple values and TIPL frames"

  16 avril, par Michael Niedermayer

  Revert "lavf/id3v2dec : support multiple values and TIPL frames"
  see : Re : [FFmpeg-devel] [PATCH 2/2] avformat/id3v2 : Check that decode_str() did advance
  but in short, first our API since 16years says we dont have multiple values per key
  
  (which it supports since 9 years only)
  and it causes some problems for ffprobe apparently.
  
  I do believe the original patch is the correct direction but it requires
  
  more changes. So revert this until other things are in place and until
  
  we have a consensus.
  This reverts commit 80b77e8e8d0630710ad6069133f397459015f139.
  

  • [DH] libavformat/id3v2.c