captionbob.effects.swipe_from_left

Swipe from left effect: a caption comes in from the left and fades out.

A caption shows a few words. It starts at the time at which its first word is spoken, outside the left edge of the video. In the first part of its time it moves to the middle of the video, fast at the start and slow at the end. Then it stays in the middle. In the last part of its time it fades out.

The swipe of a caption is a row of events of the script that follow one another, and each event is one straight move. One more event holds the caption in the middle and fades it out. 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 swipe of the four swipe effects and the common part of the effects are in effect_common.py.

Source file: captionbob/effects/swipe_from_left.py

Settings

The command line and the HTTP API call this effect the style swipe_from_left. Its settings class is SwipeFromLeftSettings. 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.
swipe_in_part	number	0.3	The part of the time of a caption, at its start, in which it moves from the edge of the video to the middle, from 0 to 1. 0 shows the caption in the middle at once.
fade_out_part	number	0.3	The part of the time of a caption, at its end, in which it fades out, from 0 to 1. 0 gives a caption that leaves with no fade. The two parts together are at most 1.
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.

SwipeFromLeftSettings

@dataclass(frozen=True)
class SwipeFromLeftSettings(SwipeSettings)

The look and the timing of the swipe from left effect.

The settings of SwipeSettings come first: the word counts, the font, the colors, the stroke, the bottom position, the side margin, the swipe in part and the fade out part. The hold time follows them. In this effect the side margins are those of a caption that sits in the middle. One word that is wider than the room between them has its end in the video when its caption starts. The swipe in part is the time in which a caption moves from the left edge to the middle.

Args:

• 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 the two parts together are above 1, when a color is not in the form "#RRGGBB", or when the font name is empty or holds a comma.

SwipeFromLeftEffect

class SwipeFromLeftEffect
    def __init__(self, settings: SwipeFromLeftSettings) -> None

Builds the ASS script that brings each caption in from the left.

Args:

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

SwipeFromLeftEffect.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 shows from the start of 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. The swipe in part of this time, in whole centiseconds, is cut into events that follow one another, and each event is one straight move of the caption. One more event holds the caption in the middle for the rest of the time and fades it out.

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.