time.pipe.ts

import { Pipe, PipeTransform } from '@angular/core';

/**
 * the TimePipe transforms n seconds to hh:mm:ss
 * or in case of zero hours to mm:ss
 */
@Pipe({
    name: 'appTime'
})
export class TimePipe implements PipeTransform {

    transform(value: number): string {

        const dateObj: Date = new Date(value * 1000);
        const hours: number = dateObj.getUTCHours();
        const minutes = dateObj.getUTCMinutes();
        const seconds = dateObj.getSeconds();

        if (hours === 0) {
            return minutes.toString().padStart(2, '0') + ':' +
                seconds.toString().padStart(2, '0');
        } else {
            return hours.toString().padStart(2, '0') + ':' +
                minutes.toString().padStart(2, '0') + ':' +
                seconds.toString().padStart(2, '0');
        }

    }

}