{
  "id": "playback-speed",
  "version": "892bb29dc280",
  "status": "published",
  "name": "Playback Speed Calculator",
  "question": "How long at this playback speed?",
  "summary": "Works out how long a video, podcast or lecture takes at a playback speed such as 1.5× or 2×, and the time saved, or the speed you need to finish it in the time you have.",
  "category": "everyday-life",
  "url": "https://www.acalculator.org/everyday-life/playback-speed-calculator",
  "markdown": "https://www.acalculator.org/everyday-life/playback-speed-calculator.md",
  "kind": "function",
  "method": "time at speed = length ÷ speed, rounded half up to the second; speed needed = length ÷ time you have.",
  "assumptions": [
    "The whole recording plays at one speed, with no skipped parts or pauses.",
    "Times are shown to the nearest second, a half second rounded up; the time saved is the difference of the shown times.",
    "Players offer set speeds (often 0.25× to 2×, some up to 3× or more); round the speed you need up to one your player has."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "find": {
        "title": "Find",
        "description": "The new time at a speed, or the speed that fits the time you have.",
        "type": "string",
        "enum": [
          "time",
          "speed"
        ]
      },
      "h": {
        "title": "Hours",
        "description": "The hours part of the length at normal speed.",
        "type": "integer",
        "minimum": 0,
        "maximum": 10000
      },
      "m": {
        "title": "Minutes",
        "description": "The minutes part of the length at normal speed.",
        "type": "integer",
        "minimum": 0,
        "maximum": 59
      },
      "s": {
        "title": "Seconds",
        "description": "The seconds part of the length at normal speed.",
        "type": "integer",
        "minimum": 0,
        "maximum": 59
      },
      "speed": {
        "title": "Playback speed",
        "description": "How many times normal speed you play at, such as 1.5 for 1.5×.",
        "type": "number",
        "minimum": 0.1,
        "maximum": 16
      },
      "th": {
        "title": "Hours",
        "description": "The hours part of the time you have.",
        "type": "integer",
        "minimum": 0,
        "maximum": 10000
      },
      "tm": {
        "title": "Minutes",
        "description": "The minutes part of the time you have.",
        "type": "integer",
        "minimum": 0,
        "maximum": 59
      },
      "ts": {
        "title": "Seconds",
        "description": "The seconds part of the time you have.",
        "type": "integer",
        "minimum": 0,
        "maximum": 59
      }
    }
  },
  "outputs": {
    "newTime": {
      "label": "Time at this speed",
      "description": "The length at normal speed ÷ the playback speed, to the nearest second.",
      "format": "duration"
    },
    "needed": {
      "label": "Speed you need",
      "description": "The length at normal speed ÷ the time you have.",
      "format": "number"
    },
    "saved": {
      "label": "Time saved",
      "description": "The length at normal speed minus the time at this speed, when faster than 1×.",
      "format": "duration"
    },
    "added": {
      "label": "Time added",
      "description": "The time at this speed minus the length at normal speed, when slower than 1×.",
      "format": "duration"
    },
    "share": {
      "label": "Share of the original time",
      "description": "The time at this speed ÷ the length at normal speed, which is 1 ÷ speed.",
      "format": "percent"
    },
    "length": {
      "label": "Length at 1×",
      "description": "The length at normal speed.",
      "format": "duration"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "find": "time",
      "h": 1,
      "m": 30,
      "s": 0,
      "speed": 1.5,
      "th": 1,
      "tm": 0,
      "ts": 0
    },
    "outputs": {
      "newTime": {
        "hours": 1,
        "minutes": 0,
        "seconds": 0
      },
      "saved": {
        "hours": 0,
        "minutes": 30,
        "seconds": 0
      },
      "share": 66.66666666666667,
      "length": {
        "hours": 1,
        "minutes": 30,
        "seconds": 0
      }
    },
    "text": "At this speed it takes 1 hour."
  },
  "examples": [
    {
      "given": {
        "find": "time",
        "h": 1,
        "m": 30,
        "s": 0,
        "speed": 1.5
      },
      "expect": {
        "newTime": {
          "hours": 1,
          "minutes": 0,
          "seconds": 0
        },
        "saved": {
          "hours": 0,
          "minutes": 30,
          "seconds": 0
        }
      },
      "source": "hand calculation in content.mdx: at speed s, a recording of length L plays in L ÷ s; 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 5,400 s ÷ 1.5 = 3,600 s"
    },
    {
      "given": {
        "find": "time",
        "h": 0,
        "m": 45,
        "s": 10,
        "speed": 1.25
      },
      "expect": {
        "newTime": {
          "hours": 0,
          "minutes": 36,
          "seconds": 8
        },
        "saved": {
          "hours": 0,
          "minutes": 9,
          "seconds": 2
        },
        "share": 80
      },
      "source": "hand calculation in content.mdx: at speed s, a recording of length L plays in L ÷ s; 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 2,710 s ÷ 1.25 = 2,168 s"
    },
    {
      "given": {
        "find": "speed",
        "h": 2,
        "m": 0,
        "s": 0,
        "th": 1,
        "tm": 20,
        "ts": 0
      },
      "expect": {
        "needed": 1.5,
        "newTime": {
          "hours": 1,
          "minutes": 20,
          "seconds": 0
        }
      },
      "source": "hand calculation in content.mdx: at speed s, a recording of length L plays in L ÷ s; 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 7,200 s ÷ 4,800 s = 1.5×"
    },
    {
      "given": {
        "find": "time",
        "h": 0,
        "m": 0,
        "s": 7,
        "speed": 2
      },
      "expect": {
        "newTime": {
          "hours": 0,
          "minutes": 0,
          "seconds": 4
        },
        "saved": {
          "hours": 0,
          "minutes": 0,
          "seconds": 3
        }
      },
      "source": "hand calculation in content.mdx: at speed s, a recording of length L plays in L ÷ s; 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 7 ÷ 2 = 3.5 s, shown as 4 s"
    }
  ],
  "sources": [
    "NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 (1 min = 60 s, 1 h = 3,600 s). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)"
  ],
  "related": [
    "audiobook-length",
    "speaking-time",
    "wpm"
  ],
  "changelog": []
}