Sur d’autres sites (11646)

• Run application in background with delete operation

  14 décembre 2016, par RoiEX

  I have the following code in my php script :

  exec ( "start ./ffmpeg.exe -i \"" . $inFile . '" "' . $outFile . '"' );
unlink ( $inFile );

  As you may have guessed, this code will not work, because ffmpeg is started, but the file is going to be deleted before ffmpeg finishes. (Or the deletion process will fail because the file is being used.)

  I want to execute ffmpeg asynchronously using start, but delete the input file on success. I tried adding && del $inFile, but this has the same effect as my code.

  For those of you who don’t know what start does ; it starts the given command in a new process, causing the exec function to return immediately.

  Any help is appreciated :)

• ffmpeg - overlay filter alpha premultiplied performs brighter on transparent images

  26 avril 2022, par windows_air

  Description

  


  I'm using ffmpeg's overlay filter with alpha premultiplied parameter. I noticed that when a completely transparent image was overlay to the background video, the output video was much brighter.

  


  In the following demo, I will use RGBA8888 format images for overlay. Its use of RGBA (255,255,255,0) indicates full transparency (aka completely transparent white), and the result demonstrates a very noticeable brightening (the expected result should be unchanged, since the image is completely transparent).
ps : Using RGBA (0,0,0,0) (aka completely transparent black) also results in a brightened image.

  


  Code (overlay transparent white)

  


  ffmpeg.exe  -loglevel debug -i a1.mp4 -i a1.png -filter_complex "[0:v][1:v]overlay=x=0:y=0:alpha=premultiplied[v]" -map "[v]"  -c:v:0 libx264 -f mp4  output.mp4


  


  result_img_white

  


  Code (overlay transparent black)

  


  This command uses lavfi to simulate the transparent black output of RGBA. For demonstration purposes only, you may need ctrl+c to prevent infinite output.

  


  ffmpeg.exe -y -i a1.mp4 -f lavfi -i "color=color=black@0.0:size=1920x540,format=rgba" -filter_complex "[0:v][1:v]overlay=x=0:y=0:alpha=premultiplied[v]" -map "[v]"  -c:v:0 libx264 -f mp4  output.mp4


  


  result_black_img

  


  The results show that the upper part is more whitish (brighter).

  


  Related files can be downloaded here : https://gist.github.com/windowsair/5315437a97dadf3f74f886486657183d

  


  ---

  


  Back to the question, I had to use premultiplied to get the correct overlay result : Using the straight option will have a darkening effect in areas that are not fully transparent, which is why I insisted on premultiplied . Is this a ffmpeg problem ? How should I avoid the undesirable effect of brighter images from transparent image overlays ? Thank you !

  


• How to route input audio to output device at realtime on Android/iOS

  6 août 2020, par Nimeth

  I'm working on Karaoke project for both Android and iOS where user could record their performances (their video and vocal) and I use ffmpeg for mixing music with their recordings. Anyway, I wish I could route/pipe user vocal at realtime (capture thru device microphone) to output device (speaker) so user could hear their voice at realtime applied with some level of echo (to produce an effect as if we were in classic karaoke room). Over weeks I have been struggling with searching the ways to implement that based on ffmpeg, but no luck. Please kindly help.

  


  Many thanks in advance.
Nimeth