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• 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

  


• 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....

  


• MSE Does not show duration when MPEG-DASH segments are created with FFmpeg

  15 mars 2023, par WaveLink

  I am trying to create a system that streams DASH segments to the browser, where it gets decoded by Media Source Extensions. When using MP4Box, the init segment loads the duration into the player, but the version generated by FFmpeg does not.

  


  I believe this is due to some sort of header missing from the init segment generated by FFmpeg, but I have not been able to figure it out. Here is the command I use to generate the files :

  


  ffmpeg -i .\source.opus -c:a libopus -c:v none -seg_duration 1 -dash_segment_type mp4 -preset ultrafast -use_timeline 1 -use_template 1 -streaming 1 -init_seg_name "segment_init.mp4" -media_seg_name "segment_$Number$.m4s" -fflags +genpts -f dash ./out.mpd
When using MP4Box, this is the config I use :

  


  MP4Box -dash 1000 -rap -profile live -segment-name "segment_$Number" .\out.mp4
In both cases, the audio does play, and both of them contain similar headers, but the FFmpeg version just does not contain the media duration in the init segment, or at least the MSE implementation cannot read it.

  


  I tested this in Chrome, Firefox, and Edge, and all of them behave the same.

  


  Thanks for any help.