====== ffmpeg - Subtitles - Add subtitles from an ASS file ======

An ASS (Advanced SubStation Alpha) file is a subtitle format that supports text styling, animation, and karaoke-like graphics.

  * ASS is a text-based subtitle format.
  * Any text editor can open .ass files.

ASS is a more advanced subtitle format than SRT since ASS allows for more advanced display features such as text positioning, fonts, animation, and graphics besides the plain text styling.

  * SRT is more popular than ASS.

ASS files have INI-style sections.

  * Each section is preceded by a line containing the sections name, in square brackets.
  * Aside from this, each line is generally composed of: a line descriptor, which tells about what the line is about; a colon; and the line data itself.
  * Any whitespace between these parts are allowed.
  * Blank lines are also allowed.
  * Hard comment lines are preceded by either a semicolon or !: (with "!" as the line descriptor).
  * Unrecognized and incorrect line formats are ignored. 

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===== Adding Soft Subtitles =====

<code bash>
ffmpeg -i input.mp4 -i subtitle.ass -c copy -c:s mov_text -metadata:s:s:0 language=eng output.mp4

ffmpeg -i input.mp4 -i subtitle.ass -c copy -c:s srt -metadata:s:s:0 language=eng output.mkv
</code>

<WRAP info>
**NOTE:**  Different syntax is used for MP4 and MKV.

  * **-c** copy specifies that the video is not to be re-encoded.
  * **-c:s mov_text** sets the ASS file to MOV_TEXT format for MP4.
  * **-c:s srt** sets the ASS file to SRT format for MKV.
  * **-metadata:s:s:0** means to set the metadata for Stream:Subtitle:Number of stream, starting with 0.
  * **language=eng** sets the subtitle language to English.
    * The value for this option uses the [[https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes|ISO 639]] language code which consists of 3 letters for every language.

</WRAP>

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===== Adding Hard Subtitles =====

<code bash>
ffmpeg -i input.mp4 -vf ass=subtitle.ass output.mp4
</code>

<WRAP info>
**NOTE:**  The subtitles will be added to the video using the default font styles.

  * **-vf** is an alias for **-filter:v**.
  * **ass=subtitle.ass** is the name of the filter followed by the name of the ASS subtitle file.

</WRAP>

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===== References =====

https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes