GI.GstBase.Objects.BaseParse

This base class is for parser elements that process data and splits it into separate audio/video/whatever frames.

It provides for:

• provides one sink pad and one source pad
• handles state changes
• can operate in pull mode or push mode
• handles seeking in both modes
• handles events (SEGMENT/EOS/FLUSH)
• handles queries (POSITION/DURATION/SEEKING/FORMAT/CONVERT)
• handles flushing

The purpose of this base class is to provide the basic functionality of a parser and share a lot of rather complex code.

Description of the parsing mechanism:

Set-up phase

• BaseParse calls BaseParseClass.start() to inform subclass that data processing is about to start now.

• BaseParse class calls BaseParseClass.set_sink_caps() to inform the subclass about incoming sinkpad caps. Subclass could already set the srcpad caps accordingly, but this might be delayed until calling baseParseFinishFrame with a non-queued frame.
• At least at this point subclass needs to tell the BaseParse class how big data chunks it wants to receive (minimum frame size ). It can do this with baseParseSetMinFrameSize.
• BaseParse class sets up appropriate data passing mode (pull/push) and starts to process the data.

Parsing phase

• BaseParse gathers at least min_frame_size bytes of data either by pulling it from upstream or collecting buffers in an internal Adapter.

• A buffer of (at least) min_frame_size bytes is passed to subclass with BaseParseClass.handle_frame(). Subclass checks the contents and can optionally return GST_FLOW_OK along with an amount of data to be skipped to find a valid frame (which will result in a subsequent DISCONT). If, otherwise, the buffer does not hold a complete frame, BaseParseClass.handle_frame() can merely return and will be called again when additional data is available. In push mode this amounts to an additional input buffer (thus minimal additional latency), in pull mode this amounts to some arbitrary reasonable buffer size increase.

Of course, baseParseSetMinFrameSize could also be used if a very specific known amount of additional data is required. If, however, the buffer holds a complete valid frame, it can pass the size of this frame to baseParseFinishFrame.

If acting as a converter, it can also merely indicate consumed input data while simultaneously providing custom output data. Note that baseclass performs some processing (such as tracking overall consumed data rate versus duration) for each finished frame, but other state is only updated upon each call to BaseParseClass.handle_frame() (such as tracking upstream input timestamp).

Subclass is also responsible for setting the buffer metadata (e.g. buffer timestamp and duration, or keyframe if applicable). (although the latter can also be done by BaseParse if it is appropriately configured, see below). Frame is provided with timestamp derived from upstream (as much as generally possible), duration obtained from configuration (see below), and offset if meaningful (in pull mode).

Note that BaseParseClass.handle_frame() might receive any small amount of input data when leftover data is being drained (e.g. at EOS).

• As part of finish frame processing, just prior to actually pushing the buffer in question, it is passed to BaseParseClass.pre_push_frame() which gives subclass yet one last chance to examine buffer metadata, or to send some custom (tag) events, or to perform custom (segment) filtering.
• During the parsing process BaseParseClass will handle both srcpad and sinkpad events. They will be passed to subclass if BaseParseClass.event() or BaseParseClass.src_event() implementations have been provided.

Shutdown phase

• BaseParse class calls BaseParseClass.stop() to inform the subclass that data parsing will be stopped.

Subclass is responsible for providing pad template caps for source and sink pads. The pads need to be named "sink" and "src". It also needs to set the fixed caps on srcpad, when the format is ensured (e.g. when base class calls subclass' BaseParseClass.set_sink_caps() function).

This base class uses FormatDefault as a meaning of frames. So, subclass conversion routine needs to know that conversion from FormatTime to FormatDefault must return the frame number that can be found from the given byte position.

BaseParse uses subclasses conversion methods also for seeking (or otherwise uses its own default one, see also below).

Subclass start and stop functions will be called to inform the beginning and end of data processing.

Things that subclass need to take care of:

• Provide pad templates
• Fixate the source pad caps when appropriate
• Inform base class how big data chunks should be retrieved. This is done with baseParseSetMinFrameSize function.
• Examine data chunks passed to subclass with BaseParseClass.handle_frame() and pass proper frame(s) to baseParseFinishFrame, and setting src pad caps and timestamps on frame.
• Provide conversion functions
• Update the duration information with baseParseSetDuration
• Optionally passthrough using baseParseSetPassthrough
• Configure various baseparse parameters using baseParseSetAverageBitrate, baseParseSetSyncable and baseParseSetFrameRate.
• In particular, if subclass is unable to determine a duration, but parsing (or specs) yields a frames per seconds rate, then this can be provided to BaseParse to enable it to cater for buffer time metadata (which will be taken from upstream as much as possible). Internally keeping track of frame durations and respective sizes that have been pushed provides BaseParse with an estimated bitrate. A default BaseParseClass.convert() (used if not overridden) will then use these rates to perform obvious conversions. These rates are also used to update (estimated) duration at regular frame intervals.

Exported types

newtype BaseParse

Memory-managed wrapper type.

Constructors

BaseParse (ManagedPtr BaseParse)

Instances

GObject BaseParse

Defined in GI.GstBase.Objects.BaseParse

Methods

gobjectType :: IO GType

HasParentTypes BaseParse

Defined in GI.GstBase.Objects.BaseParse

type ParentTypes BaseParse

Defined in GI.GstBase.Objects.BaseParse

type ParentTypes BaseParse = Element ': (Object ': (Object ': ([] :: [Type])))

class (GObject o, IsDescendantOf BaseParse o) => IsBaseParse o

Type class for types which can be safely cast to BaseParse, for instance with toBaseParse.

Instances

(GObject o, IsDescendantOf BaseParse o) => IsBaseParse o

Defined in GI.GstBase.Objects.BaseParse

toBaseParse :: (MonadIO m, IsBaseParse o) => o -> m BaseParse

Cast to BaseParse, for types for which this is known to be safe. For general casts, use castTo.

noBaseParse :: Maybe BaseParse

A convenience alias for Nothing :: Maybe BaseParse.

Methods

addIndexEntry

baseParseAddIndexEntry

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> Word64

offset: offset of entry

-> Word64

ts: timestamp associated with offset

-> Bool

key: whether entry refers to keyframe

-> Bool

force: add entry disregarding sanity checks

-> m Bool

Returns: Bool indicating whether entry was added

Adds an entry to the index associating offset to ts. It is recommended to only add keyframe entries. force allows to bypass checks, such as whether the stream is (upstream) seekable, another entry is already "close" to the new entry, etc.

convertDefault

baseParseConvertDefault

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> Format

srcFormat: Format describing the source format.

-> Int64

srcValue: Source value to be converted.

-> Format

destFormat: Format defining the converted format.

-> m (Bool, Int64)

Returns: True if conversion was successful.

Default implementation of BaseParseClass.convert().

drain

baseParseDrain

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> m ()

Drains the adapter until it is empty. It decreases the min_frame_size to match the current adapter size and calls chain method until the adapter is emptied or chain returns with error.

Since: 1.12

finishFrame

baseParseFinishFrame

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> BaseParseFrame

frame: a BaseParseFrame

-> Int32

size: consumed input data represented by frame

-> m FlowReturn

Returns: a FlowReturn that should be escalated to caller (of caller)

Collects parsed data and pushes this downstream. Source pad caps must be set when this is called.

If frame's out_buffer is set, that will be used as subsequent frame data. Otherwise, size samples will be taken from the input and used for output, and the output's metadata (timestamps etc) will be taken as (optionally) set by the subclass on frame's (input) buffer (which is otherwise ignored for any but the above purpose/information).

Note that the latter buffer is invalidated by this call, whereas the caller retains ownership of frame.

mergeTags

baseParseMergeTags

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Maybe TagList

tags: a TagList to merge, or NULL to unset previously-set tags

-> TagMergeMode

mode: the TagMergeMode to use, usually GST_TAG_MERGE_REPLACE

-> m ()

Sets the parser subclass's tags and how they should be merged with any upstream stream tags. This will override any tags previously-set with baseParseMergeTags.

Note that this is provided for convenience, and the subclass is not required to use this and can still do tag handling on its own.

Since: 1.6

pushFrame

baseParsePushFrame

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> BaseParseFrame

frame: a BaseParseFrame

-> m FlowReturn

Returns: FlowReturn

Pushes the frame's buffer downstream, sends any pending events and does some timestamp and segment handling. Takes ownership of frame's buffer, though caller retains ownership of frame.

This must be called with sinkpad STREAM_LOCK held.

setAverageBitrate

baseParseSetAverageBitrate

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> Word32

bitrate: average bitrate in bits/second

-> m ()

Optionally sets the average bitrate detected in media (if non-zero), e.g. based on metadata, as it will be posted to the application.

By default, announced average bitrate is estimated. The average bitrate is used to estimate the total duration of the stream and to estimate a seek position, if there's no index and the format is syncable (see baseParseSetSyncable).

setDuration

baseParseSetDuration

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> Format

fmt: Format.

-> Int64

duration: duration value.

-> Int32

interval: how often to update the duration estimate based on bitrate, or 0.

-> m ()

Sets the duration of the currently playing media. Subclass can use this when it is able to determine duration and/or notices a change in the media duration. Alternatively, if interval is non-zero (default), then stream duration is determined based on estimated bitrate, and updated every interval frames.

setFrameRate

baseParseSetFrameRate

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: the BaseParse to set

-> Word32

fpsNum: frames per second (numerator).

-> Word32

fpsDen: frames per second (denominator).

-> Word32

leadIn: frames needed before a segment for subsequent decode

-> Word32

leadOut: frames needed after a segment

-> m ()

If frames per second is configured, parser can take care of buffer duration and timestamping. When performing segment clipping, or seeking to a specific location, a corresponding decoder might need an initial leadIn and a following leadOut number of frames to ensure the desired segment is entirely filled upon decoding.

setHasTimingInfo

baseParseSetHasTimingInfo

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Bool

hasTiming: whether frames carry timing information

-> m ()

Set if frames carry timing information which the subclass can (generally) parse and provide. In particular, intrinsic (rather than estimated) time can be obtained following a seek.

setInferTs

baseParseSetInferTs

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Bool

inferTs: True if parser should infer DTS/PTS from each other

-> m ()

By default, the base class might try to infer PTS from DTS and vice versa. While this is generally correct for audio data, it may not be otherwise. Sub-classes implementing such formats should disable timestamp inferring.

setLatency

baseParseSetLatency

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Word64

minLatency: minimum parse latency

-> Word64

maxLatency: maximum parse latency

-> m ()

Sets the minimum and maximum (which may likely be equal) latency introduced by the parsing process. If there is such a latency, which depends on the particular parsing of the format, it typically corresponds to 1 frame duration.

setMinFrameSize

baseParseSetMinFrameSize

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: BaseParse.

-> Word32

minSize: Minimum size in bytes of the data that this base class should give to subclass.

-> m ()

Subclass can use this function to tell the base class that it needs to be given buffers of at least minSize bytes.

setPassthrough

baseParseSetPassthrough

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Bool

passthrough: True if parser should run in passthrough mode

-> m ()

Set if the nature of the format or configuration does not allow (much) parsing, and the parser should operate in passthrough mode (which only applies when operating in push mode). That is, incoming buffers are pushed through unmodified, i.e. no BaseParseClass.handle_frame() will be invoked, but BaseParseClass.pre_push_frame() will still be invoked, so subclass can perform as much or as little is appropriate for passthrough semantics in BaseParseClass.pre_push_frame().

setPtsInterpolation

baseParseSetPtsInterpolation

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Bool

ptsInterpolate: True if parser should interpolate PTS timestamps

-> m ()

By default, the base class will guess PTS timestamps using a simple interpolation (previous timestamp + duration), which is incorrect for data streams with reordering, where PTS can go backward. Sub-classes implementing such formats should disable PTS interpolation.

setSyncable

baseParseSetSyncable

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Bool

syncable: set if frame starts can be identified

-> m ()

Set if frame starts can be identified. This is set by default and determines whether seeking based on bitrate averages is possible for a format/stream.

setTsAtOffset

baseParseSetTsAtOffset

Arguments

:: (HasCallStack, MonadIO m, IsBaseParse a)

=> a

parse: a BaseParse

-> Word64

offset: offset into current buffer

-> m ()

This function should only be called from a handleFrame implementation.

BaseParse creates initial timestamps for frames by using the last timestamp seen in the stream before the frame starts. In certain cases, the correct timestamps will occur in the stream after the start of the frame, but before the start of the actual picture data. This function can be used to set the timestamps based on the offset into the frame data that the picture starts.

Since: 1.2

Properties

disablePassthrough

If set to True, baseparse will unconditionally force parsing of the incoming data. This can be required in the rare cases where the incoming side-data (caps, pts, dts, ...) is not trusted by the user and wants to force validation and parsing of the incoming data. If set to False, decision of whether to parse the data or not is up to the implementation (standard behaviour).

constructBaseParseDisablePassthrough :: IsBaseParse o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “disable-passthrough” property. This is rarely needed directly, but it is used by new.

getBaseParseDisablePassthrough :: (MonadIO m, IsBaseParse o) => o -> m Bool

Get the value of the “disable-passthrough” property. When overloading is enabled, this is equivalent to

get baseParse #disablePassthrough

setBaseParseDisablePassthrough :: (MonadIO m, IsBaseParse o) => o -> Bool -> m ()

Set the value of the “disable-passthrough” property. When overloading is enabled, this is equivalent to

set baseParse [ #disablePassthrough := value ]