vtc-ex

A SMPTE Timecode Library for Elixir

Demo

A small preview of what Vtc has to offer. Note that printing statements like inspect/1 have been elided from the examples below.

Vtc represents specific frames in a video stream as Framestamps, which can parsed from a number of different formats, including SMPTE timecode, frame count, and physical film length measured in feet and frames:

iex> Framestamp.with_seconds!(1.5, Rates.f23_98())
"<00:05:23:04 <23.98 NTSC>>"
iex> stamp = Framestamp.with_frames!("17:23:13:02", Rates.f23_98())
"<17:23:00:02 <23.98 NTSC>>"

Once in a Framestamp struct, you convert to any of the supported formats:

iex> Framestamp.smpte_timecode(stamp)
"00:05:23:04"
iex> Framestamp.frames(stamp)
1501922
iex> Framestamp.feet_and_frames(stamp)
"<93889+10 :ff35mm_4perf>"

Comparisons and kernel sorting are supported, with many helper functions for specific comparisons:

iex> Framestamp.compare(stamp, "02:00:00:00")
:gt
iex> Framestamp.gt?(stamp, "02:00:00:00")
true
iex> stamp_01 = Framestamp.with_frames!("01:00:00:00", Rates.f23_98())
iex> stamp_02 = Framestamp.with_frames!("02:00:00:00", Rates.f23_98())
iex> data_01 = %{id: 2, tc: stamp_01}
iex> data_02 = %{id: 1, tc: stamp_02}
iex> [data_02, data_01] |> Enum.sort_by(& &1.tc, Framestamp) |> inspect()
"[%{id: 2, tc: <01:00:00:00 <23.98 NTSC>>}, %{id: 1, tc: <02:00:00:00 <23.98 NTSC>>}]"

All sensible arithmetic operations are provided, such as addition, subtraction, and multiplication:

iex> stamp = Framestamp.add(tc, "01:00:00:00")
"<18:23:13:02 <23.98 NTSC>>"

You can even use native operators within special eval/2 blocks:

iex> Framestamp.eval at: 23.98 do
iex>   stamp + "00:30:00:00" * 2 - "00:15:00:00"
iex> end
"<19:08:13:02 <23.98 NTSC>>"

Ranges let you operate on in/out points, for instance, finding the overlapping area between two ranges:

iex> a_in = Framestamp.with_frames!("01:00:00:00", Rates.f23_98())
iex> a = Framestamp.Range.new!(a_in, "02:00:00:00")
"<01:00:00:00 - 02:00:00:00 :exclusive <23.98 NTSC>>"
iex> b_in = Framestamp.with_frames!("01:45:00:00", Rates.f23_98())
iex> b = Framestamp.Range.new!(b_in, "02:30:00:00")
"<01:45:00:00 - 02:30:00:00 :exclusive <23.98 NTSC>>"
iex> Framestamp.Range.intersection!(a, b)
"<01:45:00:00 - 02:00:00:00 :exclusive <23.98 NTSC>>"

Ecto types

Vtx ships with optional ecto types that can be used to accelerate you timecode workflow at the database level:

## Migration file

defmodule MyApp.MySchema do
  @moduledoc false
  use Ecto.Migration

  alias Vtc.Ecto.Postgres.PgFramestamp
  alias Vtc.Framestamp

  def change do
    create table("my_table", primary_key: false) do
      add(:id, :uuid, primary_key: true, null: false)
      add(:a, Framestamp.type())
      add(:b, Framestamp.type())
    end
  end
end

## Schema file

defmodule Vtc.Test.Support.FramestampSchema01 do
  @moduledoc false
  use Ecto.Schema

  alias Ecto.Changeset
  alias Vtc.Framestamp

  @type t() :: %__MODULE__{
          id: Ecto.UUID.t(),
          stamp_in: Framestamp.t(),
          stamp_out: Framestamp.t()
        }

  @primary_key {:id, Ecto.UUID, autogenerate: true}

  schema "my_table" do
    field(:start, Framestamp)
    field(:end, Framestamp)
  end

  @spec changeset(%__MODULE__{}, %{atom() => any()}) :: Changeset.t(%__MODULE__{})
  def changeset(schema, attrs), do: Changeset.cast(schema, attrs, [:id, :stamp_in, :stamp_out])
end

Values can be used in Ecto queries using the type/2 function. Vtc registers native operators for each type, so you can write queries like you would expect to:

iex> one_hour = Framestamp.with_frames("01:00:00:00", Rates.f23_98())
iex> 
iex> EdlEvents
iex> |> where([event], event.stamp_in > type(^one_hour, Framestamp))
iex> |> select([event], {event, event.stamp_out - event.stamp_in})

The above query finds all events with a start time greater than 01:00:00:00 and returns the record AND its calculated duration.

Goals

Offer a comprehensive set of tools for parsing, manipulating and rendering timecode with all it's quirks and incarnations.
Define an intuitive, idiomatic Elixir API.
Do all calculations in Rational representation, so there is both no drift or rounding errors when manipulating NTSC timecode, and we can represent time as finely as possible rather than being limited to the granularity of frame numbers.
Be approachable for newcomers to the timecode problem space. Each function and concept in the API Reference includes a primer on what it is and where it is used in Film and Television workflow.
Offer a flexible set of tools that support both rigorous, production-quality code and quick scratch scripts.

Features

Attributions

Drop-frame calculations adapted from David Heidelberger's blog.

35mm, 2perf and 16mm format support based on Jamie Hardt's work for vtc-rs.

Logo made by Freepik from www.flaticon.com.

Installation

If available in Hex, the package can be installed by adding vtc to your list of dependencies in mix.exs:

def deps do
  [
    {:vtc, "~> 0.14"}
  ]
end

opencinemac / vtc-ex