Description of the parsing mechanism:

gst_base_parse_merge_tags ()

void
gst_base_parse_merge_tags (GstBaseParse *parse,
                           GstTagList *tags,
                           GstTagMergeMode mode);

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 gst_base_parse_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.

Since: 1.6

gst_base_parse_set_duration ()

void
gst_base_parse_set_duration (GstBaseParse *parse,
                             GstFormat fmt,
                             gint64 duration,
                             gint interval);

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.

gst_base_parse_set_average_bitrate ()

void
gst_base_parse_set_average_bitrate (GstBaseParse *parse,
                                    guint bitrate);

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 gst_base_parse_set_syncable()).

gst_base_parse_set_min_frame_size ()

void
gst_base_parse_set_min_frame_size (GstBaseParse *parse,
                                   guint min_size);

Subclass can use this function to tell the base class that it needs to give at least min_size buffers.

gst_base_parse_set_passthrough ()

void
gst_base_parse_set_passthrough (GstBaseParse *parse,
                                gboolean passthrough);

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 check_valid_frame or parse_frame callbacks will be invoked, but pre_push_frame will still be invoked, so subclass can perform as much or as little is appropriate for passthrough semantics in pre_push_frame .

gst_base_parse_set_syncable ()

void
gst_base_parse_set_syncable (GstBaseParse *parse,
                             gboolean syncable);

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.

gst_base_parse_set_has_timing_info ()

void
gst_base_parse_set_has_timing_info (GstBaseParse *parse,
                                    gboolean has_timing);

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.

gst_base_parse_drain ()

void
gst_base_parse_drain (GstBaseParse *parse);

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

gst_base_parse_set_frame_rate ()

void
gst_base_parse_set_frame_rate (GstBaseParse *parse,
                               guint fps_num,
                               guint fps_den,
                               guint lead_in,
                               guint lead_out);

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.

gst_base_parse_set_latency ()

void
gst_base_parse_set_latency (GstBaseParse *parse,
                            GstClockTime min_latency,
                            GstClockTime max_latency);

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.

gst_base_parse_set_infer_ts ()

void
gst_base_parse_set_infer_ts (GstBaseParse *parse,
                             gboolean infer_ts);

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.

gst_base_parse_set_pts_interpolation ()

void
gst_base_parse_set_pts_interpolation (GstBaseParse *parse,
                                      gboolean pts_interpolate);

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.

gst_base_parse_set_ts_at_offset ()

void
gst_base_parse_set_ts_at_offset (GstBaseParse *parse,
                                 gsize offset);

This function should only be called from a handle_frame implementation.

GstBaseParse 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

gst_base_parse_convert_default ()

gboolean
gst_base_parse_convert_default (GstBaseParse *parse,
                                GstFormat src_format,
                                gint64 src_value,
                                GstFormat dest_format,
                                gint64 *dest_value);

Default implementation of "convert" vmethod in GstBaseParse class.

gst_base_parse_add_index_entry ()

gboolean
gst_base_parse_add_index_entry (GstBaseParse *parse,
                                guint64 offset,
                                GstClockTime ts,
                                gboolean key,
                                gboolean force);

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.

gst_base_parse_frame_new ()

GstBaseParseFrame *
gst_base_parse_frame_new (GstBuffer *buffer,
                          GstBaseParseFrameFlags flags,
                          gint overhead);

Allocates a new GstBaseParseFrame. This function is mainly for bindings, elements written in C should usually allocate the frame on the stack and then use gst_base_parse_frame_init() to initialise it.

gst_base_parse_frame_init ()

void
gst_base_parse_frame_init (GstBaseParseFrame *frame);

Sets a GstBaseParseFrame to initial state. Currently this means all public fields are zero-ed and a private flag is set to make sure gst_base_parse_frame_free() only frees the contents but not the actual frame. Use this function to initialise a GstBaseParseFrame allocated on the stack.

gst_base_parse_frame_free ()

void
gst_base_parse_frame_free (GstBaseParseFrame *frame);

gst_base_parse_push_frame ()

GstFlowReturn
gst_base_parse_push_frame (GstBaseParse *parse,
                           GstBaseParseFrame *frame);

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.

gst_base_parse_finish_frame ()

GstFlowReturn
gst_base_parse_finish_frame (GstBaseParse *parse,
                             GstBaseParseFrame *frame,
                             gint size);

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 .

GST_BASE_PARSE_DRAINING()

#define GST_BASE_PARSE_DRAINING(parse)  (!!(GST_BASE_PARSE_CAST(parse)->flags & GST_BASE_PARSE_FLAG_DRAINING))

Obtains current drain status (ie. whether EOS has been received and the parser is now processing the frames at the end of the stream)

GST_BASE_PARSE_LOST_SYNC()

#define GST_BASE_PARSE_LOST_SYNC(parse) (!!(GST_BASE_PARSE_CAST(parse)->flags & GST_BASE_PARSE_FLAG_LOST_SYNC))

Obtains current sync status.

GST_BASE_PARSE_SINK_PAD()

#define GST_BASE_PARSE_SINK_PAD(obj)    (GST_BASE_PARSE_CAST (obj)->sinkpad)

Gives the pointer to the sink GstPad object of the element.

GST_BASE_PARSE_SRC_PAD()

#define GST_BASE_PARSE_SRC_PAD(obj)    (GST_BASE_PARSE_CAST (obj)->srcpad)

Gives the pointer to the source GstPad object of the element.

struct GstBaseParse

struct GstBaseParse {
  GstElement     element;
};

The opaque GstBaseParse data structure.

struct GstBaseParseClass

struct GstBaseParseClass {
  GstElementClass parent_class;

  /* virtual methods for subclasses */

  gboolean      (*start)              (GstBaseParse * parse);

  gboolean      (*stop)               (GstBaseParse * parse);

  gboolean      (*set_sink_caps)      (GstBaseParse * parse,
                                       GstCaps      * caps);

  GstFlowReturn (*handle_frame)       (GstBaseParse      * parse,
                                       GstBaseParseFrame * frame,
                                       gint              * skipsize);

  GstFlowReturn (*pre_push_frame)     (GstBaseParse      * parse,
                                       GstBaseParseFrame * frame);

  gboolean      (*convert)            (GstBaseParse * parse,
                                       GstFormat      src_format,
                                       gint64         src_value,
                                       GstFormat      dest_format,
                                       gint64       * dest_value);

  gboolean      (*sink_event)         (GstBaseParse * parse,
                                       GstEvent     * event);

  gboolean      (*src_event)          (GstBaseParse * parse,
                                       GstEvent     * event);

  GstCaps *     (*get_sink_caps)      (GstBaseParse * parse,
                                       GstCaps      * filter);

  GstFlowReturn (*detect)             (GstBaseParse * parse,
                                       GstBuffer    * buffer);

  gboolean      (*sink_query)         (GstBaseParse * parse,
                                       GstQuery     * query);

  gboolean      (*src_query)          (GstBaseParse * parse,
                                       GstQuery     * query);
};

Subclasses can override any of the available virtual methods or not, as needed. At minimum handle_frame needs to be overridden.

GstBaseParseFrame

typedef struct {
  GstBuffer * buffer;
  GstBuffer * out_buffer;
  guint       flags;
  guint64     offset;
  gint        overhead;
} GstBaseParseFrame;

Frame (context) data passed to each frame parsing virtual methods. In addition to providing the data to be checked for a valid frame or an already identified frame, it conveys additional metadata or control information from and to the subclass w.r.t. the particular frame in question (rather than global parameters). Some of these may apply to each parsing stage, others only to some a particular one. These parameters are effectively zeroed at start of each frame's processing, i.e. parsing virtual method invocation sequence.

enum GstBaseParseFrameFlags

Flags to be used in a GstBaseParseFrame.

GST_BASE_PARSE_FLAG_DRAINING

#define GST_BASE_PARSE_FLAG_DRAINING  (1 << 1)

GST_BASE_PARSE_FLAG_LOST_SYNC

#define GST_BASE_PARSE_FLAG_LOST_SYNC (1 << 0)

GST_BASE_PARSE_FLOW_DROPPED

#define GST_BASE_PARSE_FLOW_DROPPED     GST_FLOW_CUSTOM_SUCCESS

A GstFlowReturn that can be returned from parse_frame to indicate that no output buffer was generated, or from pre_push_frame to to forego pushing buffer.

The “disable-passthrough” property

  “disable-passthrough”      gboolean

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).

Flags: Read / Write

Default value: FALSE