:right-sidebar: True BaseParse =================================================================== .. currentmodule:: gi.repository.GstBase .. class:: BaseParse(**properties: ~typing.Any) :no-contents-entry: Superclasses: :class:`~gi.repository.Gst.Element`, :class:`~gi.repository.Gst.Object`, :class:`~gi.repository.GObject.InitiallyUnowned`, :class:`~gi.repository.GObject.Object` 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 -------------------------------------------------------------------------------- - :obj:`~gi.repository.GstBase.BaseParse` calls ``GstBaseParseClass``::start to inform subclass that data processing is about to start now. - :obj:`~gi.repository.GstBase.BaseParse` class calls ``GstBaseParseClass``::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 :func:`~gi.repository.GstBase.BaseParse.finish_frame` with a non-queued frame. - At least at this point subclass needs to tell the :obj:`~gi.repository.GstBase.BaseParse` class how big data chunks it wants to receive (minimum frame size ). It can do this with :func:`~gi.repository.GstBase.BaseParse.set_min_frame_size`. - :obj:`~gi.repository.GstBase.BaseParse` class sets up appropriate data passing mode (pull/push) and starts to process the data. Parsing phase -------------------------------------------------------------------------------- - :obj:`~gi.repository.GstBase.BaseParse` gathers at least min_frame_size bytes of data either by pulling it from upstream or collecting buffers in an internal :obj:`~gi.repository.GstBase.Adapter`\. - A buffer of (at least) min_frame_size bytes is passed to subclass with ``GstBaseParseClass``::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, ``GstBaseParseClass``::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, :func:`~gi.repository.GstBase.BaseParse.set_min_frame_size` 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 :func:`~gi.repository.GstBase.BaseParse.finish_frame`. 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 ``GstBaseParseClass``::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 :obj:`~gi.repository.GstBase.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 ``GstBaseParseClass``::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 ``GstBaseParseClass``::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 ``GstBaseParseClass`` will handle both srcpad and sinkpad events. They will be passed to subclass if ``GstBaseParseClass``::sink_event or ``GstBaseParseClass``::src_event implementations have been provided. Shutdown phase -------------------------------------------------------------------------------- - :obj:`~gi.repository.GstBase.BaseParse` class calls ``GstBaseParseClass``::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' ``GstBaseParseClass``::set_sink_caps function). This base class uses %GST_FORMAT_DEFAULT as a meaning of frames. So, subclass conversion routine needs to know that conversion from %GST_FORMAT_TIME to %GST_FORMAT_DEFAULT must return the frame number that can be found from the given byte position. :obj:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.BaseParse.set_min_frame_size` function. - Examine data chunks passed to subclass with ``GstBaseParseClass``::handle_frame and pass proper frame(s) to :func:`~gi.repository.GstBase.BaseParse.finish_frame`, and setting src pad caps and timestamps on frame. - Provide conversion functions - Update the duration information with :func:`~gi.repository.GstBase.BaseParse.set_duration` - Optionally passthrough using :func:`~gi.repository.GstBase.BaseParse.set_passthrough` - Configure various baseparse parameters using :func:`~gi.repository.GstBase.BaseParse.set_average_bitrate`, :func:`~gi.repository.GstBase.BaseParse.set_syncable` and :func:`~gi.repository.GstBase.BaseParse.set_frame_rate`. - 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 :obj:`~gi.repository.GstBase.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 :obj:`~gi.repository.GstBase.BaseParse` with an estimated bitrate. A default ``GstBaseParseClass``::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. Methods ------- .. rst-class:: interim-class .. class:: BaseParse :no-index: .. method:: add_index_entry(offset: int, ts: int, key: bool, force: bool) -> bool 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. :param offset: offset of entry :param ts: timestamp associated with offset :param key: whether entry refers to keyframe :param force: add entry disregarding sanity checks .. method:: convert_default(src_format: ~gi.repository.Gst.Format, src_value: int, dest_format: ~gi.repository.Gst.Format) -> ~typing.Tuple[bool, int] Default implementation of ``GstBaseParseClass``::convert. :param src_format: :obj:`~gi.repository.Gst.Format` describing the source format. :param src_value: Source value to be converted. :param dest_format: :obj:`~gi.repository.Gst.Format` defining the converted format. .. method:: do_convert(self, src_format: ~gi.repository.Gst.Format, src_value: int, dest_format: ~gi.repository.Gst.Format, dest_value: int) -> bool :param src_format: :param src_value: :param dest_format: :param dest_value: .. method:: do_detect(self, buffer: ~gi.repository.Gst.Buffer) -> ~gi.repository.Gst.FlowReturn :param buffer: .. method:: do_get_sink_caps(self, filter: ~gi.repository.Gst.Caps) -> ~gi.repository.Gst.Caps :param filter: .. method:: do_handle_frame(self, frame: ~gi.repository.GstBase.BaseParseFrame) -> ~typing.Tuple[~gi.repository.Gst.FlowReturn, int] :param frame: .. method:: do_pre_push_frame(self, frame: ~gi.repository.GstBase.BaseParseFrame) -> ~gi.repository.Gst.FlowReturn :param frame: .. method:: do_set_sink_caps(self, caps: ~gi.repository.Gst.Caps) -> bool :param caps: .. method:: do_sink_event(self, event: ~gi.repository.Gst.Event) -> bool :param event: .. method:: do_sink_query(self, query: ~gi.repository.Gst.Query) -> bool :param query: .. method:: do_src_event(self, event: ~gi.repository.Gst.Event) -> bool :param event: .. method:: do_src_query(self, query: ~gi.repository.Gst.Query) -> bool :param query: .. method:: do_start(self) -> bool .. method:: do_stop(self) -> bool .. method:: drain() -> None 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. .. versionadded:: 1.12 .. method:: finish_frame(frame: ~gi.repository.GstBase.BaseParseFrame, size: int) -> ~gi.repository.Gst.FlowReturn Collects parsed data and pushes it 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, and ``size`` amount will be flushed from the input data. The output_buffer size can differ from the consumed size indicated by ``size``\. 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``\. :param frame: a :obj:`~gi.repository.GstBase.BaseParseFrame` :param size: consumed input data represented by frame .. method:: merge_tags(tags: ~gi.repository.Gst.TagList | None, mode: ~gi.repository.Gst.TagMergeMode) -> None 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 :func:`~gi.repository.GstBase.BaseParse.merge_tags`. 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. .. versionadded:: 1.6 :param tags: a :obj:`~gi.repository.Gst.TagList` to merge, or NULL to unset previously-set tags :param mode: the :obj:`~gi.repository.Gst.TagMergeMode` to use, usually ``GST_TAG_MERGE_REPLACE`` .. method:: push_frame(frame: ~gi.repository.GstBase.BaseParseFrame) -> ~gi.repository.Gst.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. :param frame: a :obj:`~gi.repository.GstBase.BaseParseFrame` .. method:: set_average_bitrate(bitrate: int) -> None 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 :func:`~gi.repository.GstBase.BaseParse.set_syncable`). :param bitrate: average bitrate in bits/second .. method:: set_duration(fmt: ~gi.repository.Gst.Format, duration: int, interval: int) -> None 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. :param fmt: :obj:`~gi.repository.Gst.Format`\. :param duration: duration value. :param interval: how often to update the duration estimate based on bitrate, or 0. .. method:: set_frame_rate(fps_num: int, fps_den: int, lead_in: int, lead_out: int) -> None 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 ``lead_in`` and a following ``lead_out`` number of frames to ensure the desired segment is entirely filled upon decoding. :param fps_num: frames per second (numerator). :param fps_den: frames per second (denominator). :param lead_in: frames needed before a segment for subsequent decode :param lead_out: frames needed after a segment .. method:: set_has_timing_info(has_timing: bool) -> None 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. :param has_timing: whether frames carry timing information .. method:: set_infer_ts(infer_ts: bool) -> None 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. :param infer_ts: :const:`True` if parser should infer DTS/PTS from each other .. method:: set_latency(min_latency: int, max_latency: int) -> None 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. If the provided values changed from previously provided ones, this will also post a LATENCY message on the bus so the pipeline can reconfigure its global latency. :param min_latency: minimum parse latency :param max_latency: maximum parse latency .. method:: set_min_frame_size(min_size: int) -> None Subclass can use this function to tell the base class that it needs to be given buffers of at least ``min_size`` bytes. :param min_size: Minimum size in bytes of the data that this base class should give to subclass. .. method:: set_passthrough(passthrough: bool) -> None 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 ``GstBaseParseClass``::handle_frame will be invoked, but ``GstBaseParseClass``::pre_push_frame will still be invoked, so subclass can perform as much or as little is appropriate for passthrough semantics in ``GstBaseParseClass``::pre_push_frame. :param passthrough: :const:`True` if parser should run in passthrough mode .. method:: set_pts_interpolation(pts_interpolate: bool) -> None 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. :param pts_interpolate: :const:`True` if parser should interpolate PTS timestamps .. method:: set_syncable(syncable: bool) -> None 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. :param syncable: set if frame starts can be identified .. method:: set_ts_at_offset(offset: int) -> None This function should only be called from a ``handle_frame`` implementation. :obj:`~gi.repository.GstBase.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. .. versionadded:: 1.2 :param offset: offset into current buffer Properties ---------- .. rst-class:: interim-class .. class:: BaseParse :no-index: .. attribute:: props.disable_passthrough :type: bool The type of the None singleton. Virtual Methods --------------- .. rst-class:: interim-class .. class:: BaseParse :no-index: .. method:: do_convert(src_format: ~gi.repository.Gst.Format, src_value: int, dest_format: ~gi.repository.Gst.Format, dest_value: int) -> bool The type of the None singleton. :param src_format: :param src_value: :param dest_format: :param dest_value: .. method:: do_detect(buffer: ~gi.repository.Gst.Buffer) -> ~gi.repository.Gst.FlowReturn The type of the None singleton. :param buffer: .. method:: do_get_sink_caps(filter: ~gi.repository.Gst.Caps) -> ~gi.repository.Gst.Caps The type of the None singleton. :param filter: .. method:: do_handle_frame(frame: ~gi.repository.GstBase.BaseParseFrame) -> ~typing.Tuple[~gi.repository.Gst.FlowReturn, int] The type of the None singleton. :param frame: .. method:: do_pre_push_frame(frame: ~gi.repository.GstBase.BaseParseFrame) -> ~gi.repository.Gst.FlowReturn The type of the None singleton. :param frame: .. method:: do_set_sink_caps(caps: ~gi.repository.Gst.Caps) -> bool The type of the None singleton. :param caps: .. method:: do_sink_event(event: ~gi.repository.Gst.Event) -> bool The type of the None singleton. :param event: .. method:: do_sink_query(query: ~gi.repository.Gst.Query) -> bool The type of the None singleton. :param query: .. method:: do_src_event(event: ~gi.repository.Gst.Event) -> bool The type of the None singleton. :param event: .. method:: do_src_query(query: ~gi.repository.Gst.Query) -> bool The type of the None singleton. :param query: .. method:: do_start() -> bool The type of the None singleton. .. method:: do_stop() -> bool The type of the None singleton. Fields ------ .. rst-class:: interim-class .. class:: BaseParse :no-index: .. attribute:: element The parent element. .. attribute:: flags .. attribute:: priv .. attribute:: segment .. attribute:: sinkpad .. attribute:: srcpad