defmodule Vtc.Framerate do
@moduledoc """
The rate at which a video file frames are played back, measured in frames-per-second
(24/1 = 24 frames-per-second). For more on framerate and why Vtc chooses to represent
it as a rational number, see [NTSC: Framerate vs timebase](framerate_vs_timebase.html)
and [The Rational Rationale](the_rational_rationale.html)
## Struct Fields
- `playback`: The rational representation of the real-world playback speed as a
fraction in frames-per-second.
- `ntsc`: Atom representing which, if any, NTSC convention this framerate adheres to.
## Using as an Ecto Type
See [PgFramerate](`Vtc.Ecto.Postgres.PgFramerate`) for information on how to use
`Framerate` in your postgres database as a native type.
"""
use Vtc.Ecto.Postgres.Utils
alias Vtc.Ecto.Postgres.PgFramerate
alias Vtc.Framerate.ParseError
alias Vtc.Utils.DropFrame
alias Vtc.Utils.Rational
@enforce_keys [:playback, :ntsc]
defstruct [:playback, :ntsc]
# For use in functions that must validate non-nil NTSC types.
@valid_ntsc [:non_drop, :drop]
@typedoc """
Enum of `Ntsc` types.
## Values
- `:non_drop` A non-drop NTSC value.
- `:drop` A drop-frame ntsc value.
- `nil`: Not an NTSC value
For more information on NTSC standards and framerate conventions, see
[Frame.io's](frame.io)
[blog post](https://blog.frame.io/2017/07/17/timecode-and-frame-rates) on the subject.
"""
@type ntsc() :: :non_drop | :drop | nil
@typedoc """
Type of [Framerate](`Vtc.Framerate`)
"""
@type t() :: %__MODULE__{playback: Ratio.t(), ntsc: ntsc()}
@doc section: :inspect
@doc """
The rational representation of the SMPTE timecode's 'logical speed'. For more on
timebase and it's relationship to framerate, see:
[NTSC: Framerate vs timebase](framerate_vs_timebase.html).
Returned value is in frames-per-second.
"""
@spec smpte_timebase(t()) :: Ratio.t()
def smpte_timebase(%{ntsc: nil} = framerate), do: framerate.playback
def smpte_timebase(framerate), do: framerate.playback |> Rational.round() |> Ratio.new()
@doc section: :inspect
@doc """
Returns true if the value represents and NTSC framerate.
Will return true on a Framerate with an `:ntsc` value of `:non_drop` and `:drop`.
"""
@spec ntsc?(t()) :: boolean()
def ntsc?(rate)
def ntsc?(%{ntsc: ntsc}) when ntsc in @valid_ntsc, do: true
def ntsc?(_), do: false
@typedoc """
Type returned by `new/2`
"""
@type parse_result() :: {:ok, t()} | {:error, ParseError.t()}
@typedoc """
Type for `new/2` `coerce_ntsc?` option.
"""
@type new_opt_coerce_ntsc?() :: boolean() | :if_trunc
@typedoc """
Options for `new/2` and `new!/2`.
"""
@type new_opts() :: [
ntsc: ntsc(),
coerce_ntsc?: new_opt_coerce_ntsc?(),
allow_float?: boolean(),
invert?: boolean()
]
@doc section: :parse
@doc """
Creates a new Framerate with a playback speed or timebase.
## Arguments
- `rate`: Either the playback rate or timebase. For NTSC framerates, the value will
be rounded to the nearest correct value.
## Options
- `ntsc`: Atom representing the which (or whether an) NTSC standard is being used.
Default: `nil`.
- `coerce_ntsc?`: If and how to coerce values to the nearest NTSC value.
Default: `false`
- `true`: If `ntsc` is non-nil, values will be coerced to the
nearest valid NTSC rate. So `24` would be coerced to `24000/1001`, as would
`23.98`. This option must be set to true when `ntsc` is non-nil and a float is
passed.
- `false`: Do not coerce value. Passed value must conform exactly to a valid NTSC
framerate.
- `:if_trunc`: Will coerce value to a valid NTSC rate using the `ntsc` opt value
*if* the below criteria are met. If the criteria are not met, the value will be
parsed *as-is* with `ntsc` set to `nil`:
- The incoming value is a float, with two or more significant digits that match
the truncated+rounded form. So `23.98` and `23.976` would be coerced to
`24000/1001` but `23.99` and `23.96` would both be left as-is.
- The incoming value is a Rational, and precisely represents a valid NTSC
framerate.
- The incoming value is a Rational, that when cast to float, matches the above
criteria.
- The incoming value is a string representation of any of the above.
- `allow_fractional_float?`: If `true`, will allow non-integer float values to be
converted to Rational values when parsing framerates. Can be combined with
`:if_trunc` to parse floating point values, coercing to NTSC if it appears to be
an abbreviated NTSC value.
- `invert?`: If `true`, the resulting rational `rate` value will be flipped so that
`1/24` becomes `24/1`. This can be helpful when you are parsing a rate given in
seconds-per-frame rather than frames-per-second. Default: `false`.
"""
@spec new(Ratio.t() | number() | String.t(), new_opts()) :: parse_result()
def new(rate, opts \\ [])
# for binaries we need to try to match integer, float, and rational string
# representations
def new(rate, opts) when is_binary(rate) do
parsers = [
&Integer.parse/1,
&Float.parse/1,
&parse_rational_string/1
]
parsers
|> Stream.map(fn parser -> parser.(rate) end)
|> Enum.find_value(:error, fn
{parsed, ""} -> parsed
_ -> false
end)
|> then(fn
:error -> {:error, %ParseError{reason: :unrecognized_format}}
value -> new(value, opts)
end)
end
def new(rate, opts), do: new_core(rate, opts)
@doc section: :parse
@doc """
As `new/2` but raises an error instead.
"""
@spec new!(Ratio.t() | number() | String.t(), new_opts()) :: t()
def new!(rate, opts \\ []) do
case new(rate, opts) do
{:ok, framerate} -> framerate
{:error, error} -> raise error
end
end
# Parses a rational string value like '24/1'. Conforms to the same API as
# `Integer.parse/1` and `Float.parse/1`.
@spec parse_rational_string(String.t()) :: {Ratio.t(), String.t()} | :error
defp parse_rational_string(binary) do
case String.split(binary, "/") do
[_, _] = split ->
split
|> Enum.map(&String.to_integer/1)
|> then(fn [x, y] -> {Ratio.new(x, y), ""} end)
_ ->
:error
end
end
# The core parser used to parse a rational or integer rate value.
@spec new_core(Ratio.t() | number(), new_opts()) :: parse_result()
defp new_core(input, opts) do
ntsc = Keyword.get(opts, :ntsc, nil)
invert? = Keyword.get(opts, :invert, false)
coerce_ntsc? = Keyword.get(opts, :coerce_ntsc?, false)
with :ok <- validate_ntsc(ntsc),
:ok <- validate_coerce_ntsc_opts(ntsc, coerce_ntsc?),
:ok <- validate_float(input, ntsc, coerce_ntsc?),
rate = Ratio.new(input),
:ok <- validate_positive(rate),
rate = invert(rate, invert?),
{:ok, rate, ntsc} <- coerce_ntsc_rate(rate, input, ntsc, coerce_ntsc?),
:ok <- validate_drop(rate, ntsc) do
{:ok, %__MODULE__{playback: rate, ntsc: ntsc}}
end
end
@zero Ratio.new(0)
# validates that the ntsc atom is one of our allowed values.
@spec validate_ntsc(ntsc()) :: :ok | {:error, ParseError.t()}
defp validate_ntsc(ntsc) when ntsc in [nil | @valid_ntsc], do: :ok
defp validate_ntsc(_), do: {:error, %ParseError{reason: :invalid_ntsc}}
# Validates that the `:coerce_ntsc?` and `:ntsc` opts are in a valid combination.
@spec validate_coerce_ntsc_opts(ntsc(), new_opt_coerce_ntsc?()) :: :ok | {:error, ParseError.t()}
defp validate_coerce_ntsc_opts(_, false), do: :ok
defp validate_coerce_ntsc_opts(ntsc, coerce_ntsc?) when ntsc in @valid_ntsc and coerce_ntsc? in [:if_trunc, true],
do: :ok
defp validate_coerce_ntsc_opts(_, _), do: {:error, %ParseError{reason: :coerce_requires_ntsc}}
# Validates that the float value can be reliably parsed given the `:ntsc` and
# `coerce_ntsc?` opts.
@spec validate_float(Ratio.t() | number(), ntsc(), new_opt_coerce_ntsc?()) :: :ok | {:error, ParseError.t()}
defp validate_float(value, ntsc, _) when not is_float(value) or ntsc in @valid_ntsc, do: :ok
defp validate_float(value, nil, _) when floor(value) == value, do: :ok
defp validate_float(_, _, coerce_ntsc?) when coerce_ntsc? in [true, :if_trunc], do: :ok
defp validate_float(_, _, _), do: {:error, %ParseError{reason: :imprecise_float}}
# Validates that the rate is positive.
@spec validate_positive(Ratio.t()) :: :ok | {:error, ParseError.t()}
defp validate_positive(rate) do
if Ratio.gt?(rate, @zero) do
:ok
else
{:error, %ParseError{reason: :non_positive}}
end
end
# Inverts the numerator and denominator of the rate if `invert` option was passed.
@spec invert(Ratio.t(), boolean()) :: Ratio.t()
defp invert(rate_rational, true), do: Ratio.new(rate_rational.denominator, rate_rational.numerator)
defp invert(rate_rational, false), do: rate_rational
# coerces a rate to the closest proper NTSC playback rate if the option is set.
@spec coerce_ntsc_rate(
Ratio.t(),
Ratio.t() | number(),
ntsc(),
new_opt_coerce_ntsc?()
) :: {:ok, Ratio.t(), ntsc() | nil} | {:error, ParseError.t()}
defp coerce_ntsc_rate(rate, _, nil, false), do: {:ok, rate, nil}
defp coerce_ntsc_rate(rate, input, ntsc, coerce?) when coerce? in [true, :if_trunc] do
rate_coerced = rate |> Rational.round() |> Ratio.new() |> Ratio.mult(Ratio.new(1000, 1001))
return_coerced? =
cond do
coerce? == true -> true
is_struct(input, Ratio) -> input == rate_coerced or coerce_close_float?(Ratio.to_float(input), rate_coerced)
is_integer(input) -> false
is_float(input) -> coerce_close_float?(input, rate_coerced)
end
cond do
return_coerced? -> {:ok, rate_coerced, ntsc}
coerce? == :if_trunc -> {:ok, rate, nil}
true -> {:error, %ParseError{reason: :invalid_ntsc_rate}}
end
end
defp coerce_ntsc_rate(rate, _, ntsc, false) do
whole_frame = Rational.round(rate)
if Ratio.new(whole_frame * 1000, 1001) == rate do
{:ok, rate, ntsc}
else
{:error, %ParseError{reason: :invalid_ntsc_rate}}
end
end
# Checks if a float is close enough to a valid NTSC representation to be coerced when
# `:coerce_ntsc?` is set to `:if_trunc`.
@spec coerce_close_float?(float(), Ratio.t()) :: boolean()
defp coerce_close_float?(input, rate_coerced) do
float_str = Float.to_string(input)
[_, digits] = String.split(float_str, ".")
digit_count = String.length(digits)
with true <- digit_count > 1 do
coerced_float = rate_coerced.numerator / rate_coerced.denominator
expected_string = coerced_float |> Float.round(digit_count) |> Float.to_string()
float_str == expected_string
end
end
# validates that a rate is a proper drop-frame framerate.
@spec validate_drop(Ratio.t(), ntsc()) :: :ok | {:error, ParseError.t()}
defp validate_drop(rate, :drop) do
if DropFrame.drop_allowed?(rate) do
:ok
else
{:error, %ParseError{reason: :bad_drop_rate}}
end
end
defp validate_drop(_, _), do: :ok
when_pg_enabled do
use Ecto.Type
@doc section: :ecto_migrations
@doc """
The database type for [PgFramerate](`Vtc.Ecto.Postgres.PgFramerate`).
Can be used in migrations as the fields type.
"""
@impl Ecto.Type
@spec type() :: atom()
defdelegate type, to: PgFramerate
@impl Ecto.Type
@spec cast(t() | %{String.t() => any()} | %{atom() => any()}) :: {:ok, t()} | :error
defdelegate cast(value), to: PgFramerate
@impl Ecto.Type
@spec load(PgFramerate.db_record()) :: {:ok, t()} | :error
defdelegate load(value), to: PgFramerate
@impl Ecto.Type
@spec dump(t()) :: {:ok, PgFramerate.db_record()} | :error
defdelegate dump(value), to: PgFramerate
end
end
defimpl Inspect, for: Vtc.Framerate do
alias Vtc.Framerate
alias Vtc.Private.DropFrame
alias Vtc.Utils.DropFrame
@spec inspect(Framerate.t(), Elixir.Inspect.Opts.t()) :: String.t()
def inspect(rate, _opts) do
float_str =
rate.playback
|> Ratio.to_float()
|> Float.round(2)
|> Float.to_string()
ntsc_string = if Framerate.ntsc?(rate), do: " NTSC", else: " fps"
"<#{float_str}#{ntsc_string}#{drop_string(rate)}>"
end
# Returns the string for tagging a framerate as drop frame or non-drop frame when
# the framerate could allow for both.
@spec drop_string(Framerate.t()) :: String.t()
defp drop_string(%{ntsc: nil}), do: ""
defp drop_string(%{ntsc: :drop}), do: " DF"
defp drop_string(%{ntsc: :non_drop} = rate) do
if DropFrame.drop_allowed?(rate.playback) do
" NDF"
else
""
end
end
end
defimpl String.Chars, for: Vtc.Framerate do
alias Vtc.Framerate
@spec to_string(Framerate.t()) :: String.t()
def to_string(term), do: inspect(term)
end
