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• Create a mkv file with colored background and containing a given audio and subtitle stream

  25 mai 2023, par rdrg109

  Table of contents

  


  

  • The context

  


  • Minimal working example

  


  • What I've tried

    

    • Create a mkv file with colored background and an audio stream

    


    • Create a mkv file with colored background, an audio stream and a subtitles stream

    


    


  


  • The question

  


  


  


  The context

  


  I have a *.flac file and a *.srt file. I want to merge those files in a MKV file, but at the same time, I want to add a video stream. I want the video stream to show a green background the entire time.

  


  


  Minimal working example

  


  For our experimentation, let's create two sample files : one *.flac file and one *.srt file.

  


  The following command creates a *.flac file that lasts 60 seconds and contains a sine wave.

  


  $ ffmpeg -y -f lavfi -i "sine=f=1000:d=60" input.flac


  


  The following command creates a *.srt file. Note that our last subtitle lasts until the sixth second, this is intended.

  


  $ cat << EOF > input.srt
1
00:00:00,000 --> 00:00:03,000
This is the first subtitle in a
SRT file.

2
00:00:03,000 --> 00:00:06,000
This is the second subtitle in a
SRT file.
EOF


  


  


  What I've tried

  


  


  Create a mkv file with colored background and an audio stream

  


  I know how to create a MKV file containing a given audio stream and a colored background as the video stream.

  


  The following command creates a MKV file containing input.flac as the audio stream and green background as the video stream. The MKV file have the same duration as input.flac.

  


  $ ffmpeg \
  -y \
  -f lavfi \
  -i color=c=green:s=2x2 \
  -i input.flac \
  -c:v libx264 \
  -c:a copy \
  -shortest \
  output.mkv


  


  The following command shows the duration of the streams in the resulting file.

  


  $ ffprobe -v error -print_format json -show_entries stream=codec_type:stream_tags=duration output.mkv | jq -r ''


  


  {
  "programs": [],
  "streams": [
    {
      "codec_type": "video",
      "tags": {
        "DURATION": "00:00:58.200000000"
      }
    },
    {
      "codec_type": "audio",
      "tags": {
        "DURATION": "00:01:00.000000000"
      }
    }
  ]
}


  


  


  Create a mkv file with colored background, an audio stream and a subtitles stream

  


  To add a subtitles stream, I just need to specify the *.srt file. However, when I do this, the duration of the video is set to the time of the last subtitle in the *.srt file. This is expected because I have used -shortest. I would get the result I'm looking for if it were possible to specify the stream that -shortest gives top priority to. I haven't found this information on the Internet.

  


  $ ffmpeg \
  -y \
  -f lavfi \
  -i color=c=green:s=2x2 \
  -i input.flac \
  -i input.srt \
  -c:v libx264 \
  -c:a copy \
  -shortest \
  output.mkv


  


  The following command shows the duration of the streams in the resulting file. Note that the maximum duration of the resulting file is 6 seconds, while in the resulting file from the previous section it was 1 minute.

  


  $ ffprobe -v error -print_format json -show_entries stream=codec_type:stream_tags=duration output.mkv | jq -r ''


  


  {
  "programs": [],
  "streams": [
    {
      "codec_type": "video",
      "tags": {
        "DURATION": "00:00:01.160000000"
      }
    },
    {
      "codec_type": "audio",
      "tags": {
        "DURATION": "00:00:03.134000000"
      }
    },
    {
      "codec_type": "subtitle",
      "tags": {
        "DURATION": "00:00:06.000000000"
      }
    }
  ]
}


  


  


  The question

  


  Given a *.flac file and a *.srt file. How to merge them in a *.mkv file so that it has the *.flac file as the audio stream, the *.srt file as the subtitles stream and a green background as the video stream ?

  


• checkasm/hevc_pel : Fix stack buffer overreads

  28 septembre 2021, par Andreas Rheinhardt

  checkasm/hevc_pel : Fix stack buffer overreads
  This patch increases several stack buffers in order to fix
  
  stack-buffer-overflows (e.g. in put_hevc_qpel_uni_hv_9 in
  
  line 814 of hevcdsp_template.c) detected with ASAN in the hevc_pel
  
  checkasm test.
  
  The buffers are increased by the minimal amount necessary
  
  in order not to mask potential future bugs.
  Reviewed-by : Martin Storsjö <martin@martin.st>
  
  Reviewed-by : "zhilizhao(赵志立)" <quinkblack@foxmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] tests/checkasm/hevc_pel.c

• FFmpeg uses too much memory when repeating split, select, overlay

  13 novembre 2020, par finefoot

  I'm running

  


  ffmpeg -i input.mp4 -filter_complex_script script.txt output.mp4


  


  with the following minimal example script :

  


  split[tmp],
select='between(t,1,2)',
select='between(n,0,1)',
[tmp]overlay=enable='between(t,1,2)':eof_action=repeat,
split[tmp],
select='between(t,3,4)',
select='between(n,0,1)',
[tmp]overlay=enable='between(t,3,4)':eof_action=repeat


  


  What I want to do is to take 1 frame at a certain position and repeat it for a certain duration, basically "pausing" the video, while overwriting to keep the same output length. In the example, I'm doing this twice : I'm using split[tmp] to get a second input stream to work on, select the time at position 00:01 with select='between(t,1,2)', select the first frame from that position with select='between(n,0,1)' and finally overlay that frame over the input. This repeats for a second time at position 00:03. I have tested this and it does exactly what I'm looking for.

  


  However, in my real script, I'm repeating this about 1000 times for different positions in the stream (and for shorter durations than 1 second) which results in running out of memory. What am I doing wrong ? What can I do to optimize ?