vsd-mp4 0.1.3

Port of mp4 parser from shaka-player project.
Documentation 
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/*
    REFERENCES
    ----------

    1. https://github.com/shaka-project/shaka-player/blob/9ce2f675d88d5de6f779f2a62a4f4af2bcc14611/lib/text/cue.js
    2. https://w3c.github.io/webvtt
    3. https://developer.mozilla.org/en-US/docs/Web/API/WebVTT_API

*/

use std::fmt::Write;

#[derive(Clone)]
pub(super) struct Cue {
    pub(super) end_time: f32,
    pub(super) _id: String,
    pub(super) payload: String,
    pub(super) settings: String,
    pub(super) start_time: f32,
}

/// Subtitles builder.
pub struct Subtitles {
    cues: Vec<Cue>,
}

impl Subtitles {
    pub(super) fn new(cues: Vec<Cue>) -> Self {
        let mut trimmed_cues: Vec<Cue> = vec![];

        for current_cue in cues {
            if !(current_cue.payload.is_empty() || (current_cue.start_time == current_cue.end_time))
            {
                if let Some(last_cue) = trimmed_cues.last() {
                    if last_cue.end_time == current_cue.start_time
                        && last_cue.settings == current_cue.settings
                        && last_cue.payload == current_cue.payload
                    {
                        let last_cue_index = trimmed_cues.len() - 1;
                        trimmed_cues.get_mut(last_cue_index).unwrap().end_time =
                            current_cue.end_time;
                        continue;
                    }
                }

                trimmed_cues.push(current_cue);
            }
        }

        Self { cues: trimmed_cues }
    }

    /// Extend these subtitles with another subtitles.
    pub fn extend(&mut self, other: Self) {
        self.cues.extend(other.cues);
    }

    /// Build subtitles in webvtt format.
    pub fn as_vtt(&self) -> String {
        let mut subtitles = "WEBVTT\n\n".to_owned();

        for cue in &self.cues {
            let _ = write!(
                subtitles,
                "{} --> {} {}\n{}\n\n",
                seconds_to_timestamp(cue.start_time, "."),
                seconds_to_timestamp(cue.end_time, "."),
                cue.settings,
                cue.payload
            );
        }

        subtitles
    }

    /// Build subtitles in subrip format.
    pub fn as_srt(&self) -> String {
        let mut subtitles = String::new();

        for (i, cue) in self.cues.iter().enumerate() {
            let _ = write!(
                subtitles,
                "{}\n{} --> {}\n{}\n\n",
                i + 1,
                seconds_to_timestamp(cue.start_time, ","),
                seconds_to_timestamp(cue.end_time, ","),
                cue.payload
            );
        }

        subtitles
    }
}

fn divmod(x: usize, y: usize) -> (usize, usize) {
    (x / y, x % y)
}

fn seconds_to_timestamp(seconds: f32, millisecond_sep: &str) -> String {
    let (seconds, milliseconds) = divmod((seconds * 1000.0) as usize, 1000);
    let (minutes, seconds) = divmod(seconds, 60);
    let (hours, minutes) = divmod(minutes, 60);
    format!(
        "{hours:02}:{minutes:02}:{seconds:02}{millisecond_sep}{milliseconds:03}"
    )
}