Metadata

file.cover

Obtain cover-art for a file. null is returned in case there is no such information.

Type:

(string) -> string
.{
  color_depth? : int,
  description? : string,
  format? : string,
  height? : int,
  mime : string,
  number_of_colors? : int?,
  picture_type? : int,
  width? : int}?

Arguments:

• (unlabeled) (of type string): File from which the cover should be obtained

metadata.artist

Extract artist from metadata.

Type:

([string * string]) -> string

Arguments:

• (unlabeled) (of type [string * string])

metadata.comment

Extract comment from metadata.

Type:

([string * string]) -> string

Arguments:

• (unlabeled) (of type [string * string])

metadata.cover

Extract cover from metadata. This function implements cover extraction for the following formats: coverart (ogg), apic (flac, mp3) and pic (mp3).

Type:

(?coverart_mime : string?, [string * string]) -> string
.{
  color_depth? : int,
  description? : string,
  format? : string,
  height? : int,
  mime : string,
  number_of_colors? : int?,
  picture_type? : int,
  width? : int}?

Arguments:

• coverart_mime (of type string?, which defaults to null): Mime type to use for "coverart" metadata. Support disabled if null.
• (unlabeled) (of type [string * string]): Metadata from which the cover should be extracted.

metadata.cover.remove

Remove cover metadata.

Type:

([string * string]) -> [string * string]

Arguments:

• (unlabeled) (of type [string * string])

metadata.deduplicate

Remove duplicate metadata in a source.

Type:

(?id : string?, ?using : [string]?, source('a)) -> source('a)
where 'a is a set of tracks to be muxed into a source

Arguments:

• id (of type string?, which defaults to "metadata.deduplicate"): Source id
• using (of type [string]?, which defaults to null): Labels to use to compare the metadata. Defaults to all of them when null.
• (unlabeled) (of type source('a) where 'a is a set of tracks to be muxed into a source): source

Methods:

• buffered (of type () -> [string * float]): Length of buffered data.
• clock (of type clock): The source's clock
• duration (of type () -> float): Estimation of the duration of the current track.
• elapsed (of type () -> float): Elapsed time in the current track.
• fallible (of type bool): Indicate if a source may fail, i.e. may not be ready to stream.
• generate_frame (of type () -> unit): Generate a frame from the source without consuming it. This can be useful in advanced cases where generating a frame is required to trigger some side effect like calculating some metadata before making a decision. You should make sure that the source is available before calling this function and it should only be called inside synchronous streaming loop callback such as on_frame!
• id (of type () -> string): Identifier of the source.
• insert_metadata (of type (?new_track : bool, [string * string]) -> unit): Dynamically insert metadata in a stream. Inserts a new track with the given metadata if new_track is true.
• is_active (of type () -> bool): true if the source is active, i.e. it is continuously animated by its own clock whenever it is ready. Typically, true for outputs and sources such as input.http.
• is_ready (of type () -> bool): Indicate if a source is ready to stream. This does not mean that the source is currently streaming, just that its resources are all properly initialized.
• is_up (of type () -> bool): Indicate that the source can be asked to produce some data at any time. This is true when the source is currently being used or if it could be used at any time, typically inside a switch or fallback.
• last_metadata (of type () -> [string * string]?): Return the last metadata from the source.
• log (of type {level : (() -> int).{set : (int) -> unit}}): Get or set the source's log level, from 1 to 5.
• register_command (of type (?usage : string?, description : string, string, ((string) -> string)) -> unit): Register a server command for this source. Command is registered under the source's id namespace when it gets up and de-registered when it gets down.
• remaining (of type () -> float): Estimation of remaining time in the current track.
• reset_last_metadata_on_track (of type (() -> bool).{set : (bool) -> unit}): If true, the source's last_metadata is reset on each new track. If a metadata is present along with the track mark, then it becomes the new last_metadata, otherwise, last_metadata becomes null`.
• seek (of type (float) -> float): Seek forward, in seconds (returns the amount of time effectively seeked).
• self_sync (of type () -> bool): Is the source currently controlling its own real-time loop.
• self_sync_description (of type () -> string):
• skip (of type () -> unit): Skip to the next track.
• time (of type () -> float): Get a source's time, based on its assigned clock.

Callbacks:

• on_frame (of type (?before : bool, synchronous : bool, (() -> unit)) -> unit): Call a given handler on frame. When before is true, callback is executed before computing the frame and after otherwise
• on_frame_checksum (of type (?before : ((string?) -> unit)?, synchronous : bool, ((cache : string?, string) -> unit)) -> unit): Call a given handler Register callbacks to compute frame checksums for debugging purposes. This is useful to track frame content changes through the streaming pipeline. The before callback is called before computing the frame with the checksum of the cached frame (if any, null otherwise). The main callback is called after computing the frame with the checksum of the generated frame and the remaining cache (if any).
• on_metadata (of type (synchronous : bool, (([string * string]) -> unit)) -> unit): Call a given handler to execute on each metadata
• on_position (of type (position : {float}, ?remaining : bool, ?allow_partial : bool, synchronous : bool, ((float, [string * string]) -> unit)) -> unit): Call a given handler on track position. If remaining is false, callback is executed when position in track is more or equal to position. If remaining is true, callback is executed when remaining time in the current track is less or equal to position. Keep in mind that elapsed time is exact while remaining time is always estimated. Remaining time is usually more accurate for file-based sources. When allow_partial is true, if the current track ends before the offset position is reached, callback is still executed
• on_shutdown (of type (synchronous : bool, (() -> unit)) -> unit): Call a given handler to be called when source shuts down
• on_track (of type (synchronous : bool, (([string * string]) -> unit)) -> unit): Call a given handler on track marks
• on_wake_up (of type (synchronous : bool, (() -> unit)) -> unit): Call a given handler to be called after the source is asked to get ready

metadata.export

Cleanup metadata for export. This is used to remove Liquidsoap's internal metadata entries before sending them. List of exported metadata is set using settings.encoder.metadata.export.set.

Type:

([string * string]) -> [string * string]

Arguments:

• (unlabeled) (of type [string * string])

metadata.filename

Extract filename from metadata.

Type:

([string * string]) -> string

Arguments:

• (unlabeled) (of type [string * string])

metadata.getter

Create a getter from a metadata: this is a string, whose value can be changed with a metadata.

Type:

(string, 'a, 'c
 .{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b}) ->
() -> string where 'a is an orderable type

Arguments:

• (unlabeled) (of type string): Initial value.
• (unlabeled) (of type anything that is an orderable type): Metadata on which the value should be updated.
• (unlabeled) (of type 'c.{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b} where 'a is an orderable type): Source containing the metadata.

metadata.getter.float

Create a float getter from a metadata: this is a float, whose value can be changed with a metadata.

Type:

(float, 'a, 'c
 .{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b}) ->
() -> float where 'a is an orderable type

Arguments:

• (unlabeled) (of type float): Initial value.
• (unlabeled) (of type anything that is an orderable type): Metadata on which the value should be updated.
• (unlabeled) (of type 'c.{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b} where 'a is an orderable type): Source containing the metadata.

metadata.getter.source.float

Create a float getter from a metadata: this is a float, whose value can be changed with a metadata. This function also returns the source.

Type:

(float, 'a, 'c
 .{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b}) ->
'c.{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b} *
(() -> float) where 'a is an orderable type

Arguments:

• (unlabeled) (of type float): Initial value.
• (unlabeled) (of type anything that is an orderable type): Metadata on which the value should be updated.
• (unlabeled) (of type 'c.{on_metadata : (synchronous : bool, ((['a * string]) -> unit)) -> 'b} where 'a is an orderable type): Source containing the metadata.

metadata.json.parse

Parse metadata from JSON object.

Type:

(string) -> [string * string] as json.object

Arguments:

• (unlabeled) (of type string)

metadata.json.stringify

Export metadata as JSON object. Cover art, if found, is extracted using metadata.cover and exported with key "cover" and exported using string.data_uri.encode.

Type:

(?coverart_mime : string?, ?base64 : bool, ?compact : bool, ?json5 : bool,
 [string * string]) -> string

Arguments:

• coverart_mime (of type string?, which defaults to null): Mime type to use for "coverart" metadata. Support disasbled if null.
• base64 (of type bool, which defaults to true)
• compact (of type bool, which defaults to false): Output compact text.
• json5 (of type bool, which defaults to false): Use json5 extended spec.
• (unlabeled) (of type [string * string])

metadata.lufs

Extract the LUFS from the metadata (in dB).

Type:

([string * string]) -> float?

Arguments:

• (unlabeled) (of type [string * string]): Metadata from which the LUFS should be extracted.

metadata.replaygain

Extract the ReplayGain from the metadata (in dB).

Type:

([string * string]) -> float?

Arguments:

• (unlabeled) (of type [string * string]): Metadata from which the ReplayGain should be extracted.

metadata.title

Extract title from metadata.

Type:

([string * string]) -> string

Arguments:

• (unlabeled) (of type [string * string])

string.apic.parse

Parse APIC ID3v2 tags (such as those obtained in the APIC tag from file.metadata.id3v2). The returned values are: mime, picture type, description, and picture data.

Type:

(string) -> string

Arguments:

• (unlabeled) (of type string): APIC data.

Methods:

• description (of type string): Description
• mime (of type string): Mime type
• picture_type (of type int): Picture type

string.pic.parse

Parse PIC ID3v2 tags (such as those obtained in the PIC tag from file.metadata.id3v2). The returned values are: format, picture type, description, and picture data.

Type:

(string) -> string

Arguments:

• (unlabeled) (of type string): PIC data.

Methods:

• description (of type string): Description
• format (of type string): Picture format
• picture_type (of type int): Picture type

track.metadata.deduplicate

Remove duplicate metadata in a track.

Type:

(?id : string?, ?using : [string]?, metadata) -> metadata

Arguments:

• id (of type string?, which defaults to "track.metadata.deduplicate")
• using (of type [string]?, which defaults to null): Labels to use to compare the metadata. Defaults to all of them when null.
• (unlabeled) (of type metadata)