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• ffmpeg : How does one designate what parts of an overlay video stream let the underlay video stream show through ?

  21 février 2023, par Walt Howard

  Stream 0 is a rotating planet created using povray. (https://www.povray.org/)

  


  Stream 1 is just a static jpeg of stars.

  


  I'm using overlay like this :

  


  nice ffmpeg -i protoplanet.mp4 -i stars.jpg \
         -filter_complex "[0:v]scale=1024:768[scaled];[1:v][scaled]overlay=0:0" \
         -movflags faststart -pix_fmt yuv420p -r 10 planet.mp4


  


  I had it working when I used the output from povray directly. I didn't have to know why that worked, because it just did. However, after adding some post processing to the planet video, the entire video has no alpha channel (educated guess) so the background stream (Stream 1) cannot show through.

  


  The post processing I did was this (which works great) : https://www.reddit.com/r/ffmpeg/comments/im2mkp/creating_a_retro_glow_effect_with_ffmpeg/

  


  But that made the video unable to have an overlay background possibly due to it destroying the alpha channel and turning many of the blacks to dark grey.

  


  I can merge the pure POVRAY output and the background and then add the glow effect, but it adds the effect to the background stars and captions also which ruins the effect to some degree. I want to glo-ify the planet first, then stick it on a pure starfield background.

  


  In thinking this over I may have to recreate the alpha channel after adding the glow effect, using a nearest match to black and dark grey to alpha.

  


  Hmmm. It might be a codec issue as I didn't specify any -c:v in any of my commands....

  


• How to show subtitle on video in ffmpeg

  19 février 2023, par Ammara

  I am working with ffmpeg. I use below code to show subtitle on video. I create video but subtitle did not show. Please help me
Here is my code. here is my abc.srt file. I store this to my download folder of mobile

  


  1&#xA;00:00:00,000 --> 00:00:01,500&#xA;This an example subtitle&#xA;&#xA;2&#xA;00:00:01,600 --> 00:00:02,500&#xA;<i>Italic style</i>&#xA;&#xA;3   &#xA;00:00:03,000 --> 00:00:15,000&#xA; Video by Tiger Lily on pexels.com&#xA;

  


  here is ffmpeg command

  


  String srt=BASE_PATH+'abc.srt';
  String CommandOverlay=' -i ${video1} -i "$srt" -c:v copy -c:a copy -c:s mov_text ${OUTPUT_PATH}';
  await FFmpegKit.execute(CommandOverlay).then((session) async {
    final returnCode = await session.getReturnCode();
    if (ReturnCode.isSuccess(returnCode)) {print("Task Completed");}
    else if (ReturnCode.isCancel(returnCode)) {print("cancel");}
    else {print("error ");}
  });
}else if (await Permission.storage.isPermanentlyDenied) {
  openAppSettings();
}


  


  It generates video without any subtitle

  


• Show video length in HLS player before all TS files are created

  14 novembre 2022, par WilliamTaco

  I have a spring-boot backend which on request (on demand) uses ffmpeg to create a m3u8 playlist with its ts files from a mp4 file. So basically my react frontend requests the index.m3u8 from the backend and if it doesnt already exist it creates it and then start serving it with its ts files. This causes the frontend HLS player to show the length of the video to the combined length of the generated chunks which gets longer as time goes on until its fully there. It totally makes sense but was wondering what the correct way of showing the full length in the player even though its not fully created yet ?

  


  Im using react-hls-player for playing the stream and spring-boot + a java ffmpeg wrapper to transcode the video.

  


  Might be thinking about this the wrong way so feel free to correct me if im in the wrong path !