Sur d’autres sites (11957)

• FFMPEG How to trim last 2 seconds of multiple files ?

  28 août 2022, par user10784270

  I have over 200 video clips each exactly 5 seconds long, however, the last 2 seconds of each are just a black screen so I want to have this trimmed out. How would I do this ?

  


• 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 !

  


• Add Padding to video

  26 juin 2023, par Akari

  I have a video which size is 576 x 1024, my screen phone is 576 x 2044. I want to make the height of video is 2044 (full screen) and add padding black background both top and bottom. What can I do ? I currently use FFmpeg library.

  


  I want to process video in android kotlin, and I use some commands but it it doesn't work.

  


  Example :

  


  fun makeVideoFullScreen(
    context: Context,
    inputVideoPath: String,
    screenWidth: Int,
    screenHeight: Int,
    listener : (outputPath: String, returnCode: Int) -> Unit
){
    val fileName = Utility.getCurrentTime()
    val externalDir = context.getExternalFilesDir(null)
    val file = File(externalDir, "temp_video${fileName}.mp4")
    val outputPath = file.absolutePath

    val cmd = arrayOf(
        "-i", inputVideoPath,
        "-vf", "scale=-1:$screenHeight, pad=$screenWidth:$screenHeight:(ow-iw)/2:(oh-ih)/2:black",
        "-c:v", "libx264",
        "-preset", "ultrafast",
        "-c:a", "copy",
        outputPath
    )

    FFmpeg.executeAsync(cmd
    ) { _, returnCode ->
        listener(outputPath, returnCode)
    }
}