captionbob.effects.typewriter

Typewriter effect: the letters of a caption appear one after the other.

A caption shows a few words. The letters of a word are typed in the first part of the time in which the word is spoken, so the typing follows the voice and each word is whole before the next word starts. A letter that is not typed yet is hidden but keeps its room, so no letter moves when the next letter appears.

Each letter is drawn on its own. So the effect is for a script whose letters do not join. The letters of a script such as Arabic would be drawn in the form that they have when they stand alone.

The effect draws nothing itself. It builds the text of an ASS script, and the ffmpeg filter ass draws the script on the video. The common part of the effects is in effect_common.py.

Source file: captionbob/effects/typewriter.py

Settings

The command line and the HTTP API call this effect the style typewriter. Its settings class is TypewriterSettings. Each setting has the default below.

Setting	Type	Default	Description
most_words	integer	3	The most words that one caption shows.
fewest_words	integer	1	The fewest words that one caption shows, when its sentence is long enough for that.
font_name	string	"DejaVu Sans"	Name of the font of the text.
font_size	integer	80	Height of the font in pixels.
bold	boolean	true	True for bold text.
primary_color	string	"#FFFFFF"	Color of the text, as "#RRGGBB".
stroke_color	string	"#000000"	Color of the outline of the text, as "#RRGGBB".
stroke_width	number	6.0	Width of the outline in pixels. 0 gives no outline.
bottom_position	number	0.75	Where the bottom of the caption sits, as a part of the video height from the top. 0.75 is three quarters of the way down.
side_margin	integer	54	Room in pixels that stays free on the left and on the right of the caption. A caption that is too wide for the room between the margins breaks into lines.
type_part	number	0.5	The part of the time of a word, at its start, in which its letters are typed, from 0 to 1. The word is whole for the rest of its time. 0 shows each word at once when it starts.
fade_seconds	number	0.1	Time in which a caption fades in, and in which it fades out. 0 gives no fade.
hold_seconds	number	0.6	The longest time that a caption stays after its last word ends. The caption goes earlier when the next caption starts.

TypewriterSettings

@dataclass(frozen=True)
class TypewriterSettings(CaptionSettings)

The look and the timing of the typewriter effect.

The settings of CaptionSettings come first: the word counts, the font, the colors, the stroke, the bottom position and the side margin. These settings follow them.

Args:

• type_part: The part of the time of a word, at its start, in which its letters are typed, from 0 to 1. The word is whole for the rest of its time. 0 shows each word at once when it starts.
• fade_seconds: Time in which a caption fades in, and in which it fades out. 0 gives no fade.
• hold_seconds: The longest time that a caption stays after its last word ends. The caption goes earlier when the next caption starts.

Raises:

• TypeError: When a word count is not a whole number.
• ValueError: When a value is outside its range, when a color is not in the form "#RRGGBB", or when the font name is empty or holds a comma.

TypewriterEffect

class TypewriterEffect
    def __init__(self, settings: TypewriterSettings) -> None

Builds the ASS script that types the captions letter by letter.

Args:

• settings: The look and the timing of the effect.

TypewriterEffect.build_ass_text

def build_ass_text(self, words: Sequence[Word], video: VideoInfo) -> str

Build the ASS script of the effect for the words of one video.

Each caption group is one event of the script. An event starts with its first word. It ends when the next caption starts, and at the latest the hold time after its last word and at the end of the video.

Args:

• words: The words of the video in time order, each with its times.
• video: The frame size and the duration of the video.

Returns:

The text of the ASS script. It has no event when there are no words.

Raises:

• ValueError: When the side margins leave no room for the caption in the width of the video.