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• How can I automatically embed commit information into a subtitles file that I'm tracking ?

  23 février 2015, par microspace

  I use git to track *.ass subtitle files.
  Here is example of *.ass file :

  [Script Info]
  
  ; Script generated by Aegisub 3.1.2
  
  ; http://www.aegisub.org/
  
  Title: Default Aegisub file
  
  ScriptType: v4.00+
  
  
  
  [V4+ Styles]
  
  Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour,    BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
  
  Style: Default,Arial,20,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,2,2,2,10,10,10,1
  
  Style: titr,DejaVu     
  
  
  
  Sans,20,&H007DDBFA,&H000000FF,&H00000000,&HFF000000,0,0,0,0,100,100,0,0,1,2,2,1,10,10,10,1
  
  
  
  [Events]
  
  Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
  
  Dialogue: 0,0:00:00.46,0:00:11.22,Default,,0,0,0,,Если это можно было бы
  
  Dialogue: 0,0:00:03.44,0:00:08.96,titr,,0,0,0,,{\pos(20,240)\fad(600,600)}бывший министр

  After commit I burn subtitles into video :

  ffmpeg -i video.avi -vf "ass=subtitle.ass" out.avi

  My goal is to show commit date for 10 second at the start of movie. This should be done automatically.

  1) It can be easily done with by modifying subtitle.ass itself, but I can’t do it after commit and there are other reasons.

  2) It can be done by ffmpeg from command line : How to use ffmpeg to add a text to avi video ?

  Problem is that in this case text will be shown for the whole lenght of movie.

  3) I can copy *.ass file to temporary directory, insert date, render and delete *.ass file.

  Is there a simpler way ?

• How to Match ASS Subtitle Font Size with Flutter Text Size for a 1080p Video ?

  16 décembre 2024, par Mostafa Fathi

  I’m working on a project where I need to synchronize the font size of ASS subtitles with the text size a user sees in a Flutter application. The goal is to ensure that the text size in a 1080p video matches what the user sees in the app.

  


  What I've Tried :

  


  

  1. Calculating font size using height ratio (PlayResY/DeviceHeight) :

  


  


  

  • I used the formula :

  


  


  FontSize_ASS = FontSize_Flutter * (PlayResY / DeviceHeight)


  


  

  • While the result seemed logical, the final output in the video was smaller than expected.

  


  


  

  2. Adding a scaling factor :

  


  


  

  • I introduced a scaling factor (around 3.0) to address the size discrepancy.

  


  • This improved the result but still felt inconsistent and lacked precision.

  


  


  

  3. Using force_style in FFmpeg :

  


  


  

  • I applied the force_style parameter to control the font size in FFmpeg directly.

  


  


  ffmpeg -i input.mp4 -vf "subtitles=subtitle.ass:force_style='FontSize=90'" -c:a copy output.mp4


  


  

  • While it produced better results, it’s not an ideal solution as it bypasses the calculations in the ASS file.

  


  


  

  4. Aligning PlayResX and PlayResY in the ASS file :
I ensured that these parameters matched the target video resolution (1920×1080) :

  


  


  PlayResX: 1920
PlayResY: 1080


  


  

  • Despite this adjustment, the font size didn’t align perfectly with the Flutter app text size.

  


  


  

  5. Reading font metrics from the font file dynamically :
To improve precision, I wrote a function in Flutter that reads font metrics (units per EM, ascender, and descender) from the TTF font file and calculates a more accurate scaling factor :

  


  


  Future readFontMetrics(
      String fontFilePath, 
      double originalFontSize,
) async {
  final fontData = await File(fontFilePath).readAsBytes();
  final fontBytes = fontData.buffer.asUint8List();
  final byteData = ByteData.sublistView(fontBytes);

  int numTables = readUInt16BE(byteData, 4);
  int offsetTableStart = 12;
  Map> tables = {};

  for (int i = 0; i < numTables; i++) {
    int recordOffset = offsetTableStart + i * 16;
    String tag =
        utf8.decode(fontBytes.sublist(recordOffset, recordOffset          + 4));
    int offset = readUInt32BE(byteData, recordOffset + 8);
    int length = readUInt32BE(byteData, recordOffset + 12);

    tables[tag] = {
      'offset': offset,
      'length': length,
    };
  }

  if (!tables.containsKey('head') || !tables.containsKey('hhea'){
    print('Required tables not found in the font file.');
    return null;
  }

  int headOffset = tables['head']!['offset']!;
  int unitsPerEm = readUInt16BE(byteData, headOffset + 18);

  int hheaOffset = tables['hhea']!['offset']!;
  int ascender = readInt16BE(byteData, hheaOffset + 4);
  int descender = readInt16BE(byteData, hheaOffset + 6);

  print('unitsPerEm: $unitsPerEm');
  print('ascender: $ascender');
  print('descender: $descender');

  int nominalSize = unitsPerEm;
  int realDimensionSize = ascender - descender;
  double scaleFactor = realDimensionSize / nominalSize;
  double realFontSize = originalFontSize * scaleFactor;

  print('Scale Factor: $scaleFactor');
  print('Real Font Size: $realFontSize');

  return realFontSize;
}


  


  

  • This function dynamically reads the font properties (ascender, descender, and unitsPerEM) and calculates a scale factor to get the real font size. Despite this effort, discrepancies persist when mapping it to the ASS font size.

  


  


  Question :
How can I ensure that the font size in the ASS file accurately reflects the size the user sees in Flutter ? Is there a reliable method to calculate or align the sizes correctly across both systems ? Any insights or suggestions would be greatly appreciated.

  


  Thank you ! 🙏

  


• ffmpeg : Input link parameters do not match the corresponding output link parameters, when concatenating same size videos

  4 mars 2021, par mSourire

  I'm trying to combine a video and an audio, using the following command :

  


  ffmpeg -y -i 1.mkv -i 1.mka 
-max_muxing_queue_size 10000 -preset veryfast -r 30 -crf 20 -b:a 96000 -vbr on
-strict experimental
-filter_complex '
color=black:s=320x240:d=7ms[black0];
aevalsrc=0:d=15ms[silence1];
[black0][0]concat=n=2:v=1:a=0[video];
[1][silence1]concat=n=2:v=0:a=1[audio]'
-map [video] -map [audio] -c:v libvpx -c:a libopus output.webm


  


  But ffmpeg returns an error :

  


  [Parsed_concat_2 @ 0x7f8004506d00] Input link in0:v0 parameters (size 640x480, SAR 1:1) do not match the corresponding output link in0:v0 parameters (320x240, SAR 1:1)
[Parsed_concat_2 @ 0x7f8004506d00] Failed to configure output pad on Parsed_concat_2
Error reinitializing filters!
Failed to inject frame into filter network: Invalid argument
Error while processing the decoded data for stream #0:0
[libopus @ 0x7f800500c000] 1 frames left in the queue on closing
Conversion failed!


  


  It looks like ffmpeg is unable to concatenate video and black frames, complaining, that video has a distinct resolution, but that's not true :

  


  #> ffprobe 1.mkv
Input #0, matroska,webm, from '1.mkv':
  Metadata:
    encoder         : GStreamer matroskamux version 1.8.1.1
    creation_time   : 2021-03-02T13:44:03.000000Z
  Duration: 00:01:48.41, start: 0.710000, bitrate: 757 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p(progressive), 320x240, SAR 1:1 DAR 4:3, 120 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : Video


  


  So, both the input source and the filter has the same resolution.

  


  When I'm trying to change the color filter to "color=s=640x480", ffmpeg says an opposite thing :

  


  [Parsed_concat_2 @ 0x7fca3ca185c0] Input link in0:v0 parameters (size 320x240, SAR 1:1) do not match the corresponding output link in0:v0 parameters (640x480, SAR 1:1)
[Parsed_concat_2 @ 0x7fca3ca185c0] Failed to configure output pad on Parsed_concat_2
Error reinitializing filters!
Failed to inject frame into filter network: Invalid argument


  


  Help please to solve this !

  


  Full listing :

  


  ffmpeg -y -i 1.mkv -i 1.mka
-max_muxing_queue_size 10000
-preset veryfast -r 30 -crf 20 -b:a 96000 -vbr on
-strict experimental
-filter_complex '
color=black:s=320x240:d=7ms[black0];
aevalsrc=0:d=15ms[silence1];
[black0][0]concat=n=2:v=1:a=0[video];
[1][silence1]concat=n=2:v=0:a=1[audio]'
-map [video] -map [audio] -c:v libvpx -c:a libopus output.webm

ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.17)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_9 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, matroska,webm, from '1.mkv':
  Metadata:
    encoder         : GStreamer matroskamux version 1.8.1.1
    creation_time   : 2021-03-02T13:44:03.000000Z
  Duration: 00:01:48.41, start: 0.710000, bitrate: 757 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p(progressive), 320x240, SAR 1:1 DAR 4:3, 120 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : Video
Input #1, matroska,webm, from '1.mka':
  Metadata:
    encoder         : GStreamer matroskamux version 1.8.1.1
    creation_time   : 2021-03-02T13:44:03.000000Z
  Duration: 00:01:48.40, start: 0.703000, bitrate: 38 kb/s
    Stream #1:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
    Metadata:
      title           : Audio
Codec AVOption preset (Configuration preset) specified for output file #0 (output.webm) has not been used for any stream. The most likely reason is either wrong type (e.g. a video option with no video streams) or that it is a private option of some encoder which was not actually used for any stream.
Stream mapping:
  Stream #0:0 (vp8) -> concat:in1:v0
  Stream #1:0 (opus) -> concat:in0:a0
  concat -> Stream #0:0 (libvpx)
  concat -> Stream #0:1 (libopus)
Press [q] to stop, [?] for help
[libvpx @ 0x7fe08a80bc00] v1.9.0
[libvpx @ 0x7fe08a80bc00] Bitrate not specified for constrained quality mode, using default of 256kbit/sec
Output #0, webm, to 'output.webm':
  Metadata:
    encoder         : Lavf58.45.100
    Stream #0:0: Video: vp8 (libvpx), yuv420p, 320x240 [SAR 1:1 DAR 4:3], q=-1--1, 256 kb/s, 30 fps, 1k tbn, 30 tbc (default)
    Metadata:
      encoder         : Lavc58.91.100 libvpx
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1: Audio: opus (libopus), 48000 Hz, stereo, flt, 96 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 libopus
[Parsed_color_0 @ 0x7fe089815940] EOF timestamp not reliable
[Parsed_concat_2 @ 0x7fe088501980] Input link in0:v0 parameters (size 640x480, SAR 1:1) do not match the corresponding output link in0:v0 parameters (320x240, SAR 1:1)
[Parsed_concat_2 @ 0x7fe088501980] Failed to configure output pad on Parsed_concat_2
Error reinitializing filters!
Failed to inject frame into filter network: Invalid argument
Error while processing the decoded data for stream #0:0
[libopus @ 0x7fe08a810c00] 1 frames left in the queue on closing
Conversion failed!