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• Cross compiling FFmpeg + Qt application with MXE

  26 mai 2016, par ldr

  I got a pretty simple project that uses Qt as well as FFmpeg that i developed under linux.
  Now I’am having trouble cross compiling said project with MXE to use it on a windows machine.

  Under linux everything i had to do was adding

  LIBS += -lavcodec -lavformat -lswscale -lavutil

  to Qt’s .pro file and wrap the includes for FFmpeg in an "extern "C"" block and it compiles just fine.

  Now for MXE i just cloned the git repo and used

  make MXE_TARGETS='x86_64-w64-mingw32.static' qt5 ffmpeg

  As the MXE doc states i set the PATH variable and used

  qmake && make

  But i get a lot of undefined reference errors regarding libavformat.

  Can anybody tell me what i am doing wrong here ? I’m kinda lost.

• FFmpeg : Issues for Transparent Background in WebM Video [closed]

  20 juillet 2024, par BlueSky

  I've encountered an issue while processing videos with FFmpeg. I want to convert a MOV video with an alpha channel to WebM format and overlay it onto a main video. Below are the steps I took and the problem I encountered.

  


  I used Adobe After Effects (AE) to remove the green screen background from a video and exported the MOV file with RGB+Alpha channels using the Animation codec. Additionally, I tried exporting in QuickTime format, both ensuring the alpha channel was included.

  


  When converting the MOV video to WebM format, I executed the following command :

  


  ffmpeg -i input.mov -c:v libvpx-vp9 overlay.webm


  


  Then, I attempted to overlay the converted WebM video onto the main video main.mp4 using the following command :

  


  ffmpeg -i main.mp4 -vf "movie=overlay.webm,scale=200x200[video_inner];[in][video_inner]overlay=x=10:y=10[out]" output.mp4


  


  However, in the final output.mp4 video, the background of the WebM video was not transparent as expected, but instead showed a black background after removing the green screen.

  


  Could there be an error in one of my steps ?

  


  I have tried different command parameters and options but have not been able to resolve this issue.

  


  I expected the WebM video to retain its transparent background when overlaid onto the main video. However, the resulting output.mp4 video showed the background of the WebM portion as black instead of transparent.

  


• Use ffmpeg to downscale, tonemap, downmix and re encode mkv

  1er février 2021, par nikartz

  I try to use ffmpeg to downscale a 4k and tonemap a 4k HDR mkv to a 1080p SDR mkv with this code :

  


  ffmpeg -i "Input.mkv" -vf zscale=t=linear:npl=100,format=gbrpf32le,zscale=p=bt709,tonemap=tonemap=hable:desat=0,zscale=t=bt709:m=bt709:r=tv,format=yuv420p -c:v hevc_nvenc -b:v 12M -preset slow "Output.mkv"


  


  The problem is, that only the first audio track (of four) is copied to the new mkv and the subtitle tracks are missing :

  


  Input :

  


  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, bt2020nc/bt2020/smpte2084), 3840x2160 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 23.98 tbc (default)
Stream #0:1(ger): Audio: eac3, 48000 Hz, 7.1, fltp (default)
Stream #0:2(ger): Audio: dts (DTS-HD MA), 48000 Hz, 7.1, s16p
Stream #0:3(eng): Audio: truehd, 48000 Hz, 7.1, s32 (24 bit)
Stream #0:4(eng): Audio: ac3, 48000 Hz, 5.1(side), fltp, 640 kb/s
Stream #0:5(ger): Subtitle: subrip (default) (forced)
Stream #0:6(ger): Subtitle: dvd_subtitle, 1920x1080 (forced)
Stream #0:7(ger): Subtitle: hdmv_pgs_subtitle, 1920x1080 (forced)
Stream #0:8(ger): Subtitle: dvd_subtitle, 1920x1080
Stream #0:9(ger): Subtitle: hdmv_pgs_subtitle
Stream #0:10(eng): Subtitle: dvd_subtitle, 1920x1080
Stream #0:11(eng): Subtitle: hdmv_pgs_subtitle


  


  Output :

  


  Stream #0:0: Video: hevc (Main), yuv420p(tv), 3840x2160 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 23.98 tbc (default)
Stream #0:1(ger): Audio: vorbis, 48000 Hz, 7.1, fltp (default)
Stream #0:2(ger): Subtitle: ass (default) (forced)


  


  I would like to have an mkv as output converts all the audio tracks to aac Stereo (but keeps all four of them), copies the subtitle tracks and tonemaps/downscales the video track.

  


  I have tried to use the -map 0 or -map 0:a:0 -map 0:a:1 ... commands (and some similiar to those, however I seemingly end up with either one audio track, no video track or a video track that is just copied.

  


  I possible, I would also like to use nvenc with a high quality preset, which is the reason for -c:v hevc_nvenc -b:v 12M -preset slow in my command, however I have no idea, if this is done right, since the ouput mkv also as a 4k video track instead of a 1080p. Maybe this is caused by the -c:v because it overrides -vf ? Sorry, I am feeling dumb and am just getting started with ffmpeg.

  


  There is so much information about ffmpeg out there, but it is either too complicated for me, or not answering my questions.

  


  Thanks for your help !