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GStreamer 0.10 Library Reference Manual | |
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| Top | Description | ||||
#include <gst/base/gstbaseparse.h> struct GstBaseParse; struct GstBaseParseClass; void gst_base_parse_set_duration (GstBaseParse *parse,GstFormat fmt,gint64 duration,gint interval); void gst_base_parse_set_average_bitrate (GstBaseParse *parse,guint bitrate); void gst_base_parse_set_min_frame_size (GstBaseParse *parse,guint min_size); void gst_base_parse_set_passthrough (GstBaseParse *parse,gboolean passthrough); void gst_base_parse_set_syncable (GstBaseParse *parse,gboolean syncable); void gst_base_parse_set_has_timing_info (GstBaseParse *parse,gboolean has_timing); void gst_base_parse_set_frame_rate (GstBaseParse *parse,guint fps_num,guint fps_den,guint lead_in,guint lead_out); gboolean gst_base_parse_convert_default (GstBaseParse *parse,GstFormat src_format,gint64 src_value,GstFormat dest_format,gint64 *dest_value); gboolean gst_base_parse_add_index_entry (GstBaseParse *parse,guint64 offset,GstClockTime ts,gboolean key,gboolean force); GstBaseParseFrame; enum GstBaseParseFrameFlags; GstBaseParseFrame * gst_base_parse_frame_new (GstBuffer *buffer,GstBaseParseFrameFlags flags,gint overhead); void gst_base_parse_frame_init (GstBaseParseFrame *frame); void gst_base_parse_frame_free (GstBaseParseFrame *frame); GstFlowReturn gst_base_parse_push_frame (GstBaseParse *parse,GstBaseParseFrame *frame); #define GST_BASE_PARSE_DRAINING (parse) #define GST_BASE_PARSE_FLAG_DRAINING #define GST_BASE_PARSE_FLAG_LOST_SYNC #define GST_BASE_PARSE_FLOW_DROPPED #define GST_BASE_PARSE_FLOW_QUEUED #define GST_BASE_PARSE_LOST_SYNC (parse) #define GST_BASE_PARSE_SINK_PAD (obj) #define GST_BASE_PARSE_SRC_PAD (obj)
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 (NEWSEGMENT/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
GstBaseParse class calls set_sink_caps to inform the subclass about
incoming sinkpad caps. Subclass should set the srcpad caps accordingly.
GstBaseParse calls start to inform subclass that data processing is
about to start now.
At least at this point subclass needs to tell the GstBaseParse class
how big data chunks it wants to receive (min_frame_size). It can do
this with gst_base_parse_set_min_frame_size().
GstBaseParse class sets up appropriate data passing mode (pull/push) and starts to process the data.
Parsing phase
GstBaseParse gathers at least min_frame_size bytes of data either by pulling it from upstream or collecting buffers in an internal GstAdapter.
A buffer of (at least) min_frame_size bytes is passed to subclass with
check_valid_frame. Subclass checks the contents and returns TRUE
if the buffer contains a valid frame. It also needs to set the
framesize according to the detected frame size. If buffer didn't
contain a valid frame, this call must return FALSE and optionally
set the skipsize value to inform base class that how many bytes
it needs to skip in order to find a valid frame. framesize can always
indicate a new minimum for current frame parsing. Indicating G_MAXUINT
for requested amount means subclass simply needs best available
subsequent data. 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. The passed buffer
is read-only. Note that check_valid_frame might receive any small
amount of input data when leftover data is being drained (e.g. at EOS).
After valid frame is found, it will be passed again to subclass with
parse_frame call. Now subclass is responsible for parsing the
frame contents and setting the caps, and buffer metadata (e.g.
buffer timestamp and duration, or keyframe if applicable).
(although the latter can also be done by GstBaseParse 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).
Finally the buffer can be pushed downstream and the parsing loop starts
over again. Just prior to actually pushing the buffer in question,
it is passed to 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 event or
src_event callbacks have been provided.
Shutdown phase
GstBaseParse class calls 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' 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.
GstBaseParse 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 gst_base_parse_set_min_frame_size() function.
Examine data chunks passed to subclass with check_valid_frame
and tell if they contain a valid frame
Set the caps and timestamp to frame that is passed to subclass with
parse_frame function.
Provide conversion functions
Update the duration information with gst_base_parse_set_duration()
Optionally passthrough using gst_base_parse_set_passthrough()
Configure various baseparse parameters using
gst_base_parse_set_average_bitrate(), gst_base_parse_set_syncable()
and gst_base_parse_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 GstBaseParse 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 GstBaseParse with an estimated
bitrate. A default convert (used if not overriden) will then use these
rates to perform obvious conversions. These rates are also used to
update (estimated) duration at regular frame intervals.
struct GstBaseParse {
GstElement element;
};
The opaque GstBaseParse data structure.
GstElement |
the parent element. |
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);
gboolean (*check_valid_frame) (GstBaseParse * parse,
GstBaseParseFrame * frame,
guint * framesize,
gint * skipsize);
GstFlowReturn (*parse_frame) (GstBaseParse * parse,
GstBaseParseFrame * frame);
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 (*event) (GstBaseParse * parse,
GstEvent * event);
gboolean (*src_event) (GstBaseParse * parse,
GstEvent * event);
GstCaps * (*get_sink_caps) (GstBaseParse * parse);
GstFlowReturn (*detect) (GstBaseParse * parse,
GstBuffer * buffer);
};
Subclasses can override any of the available virtual methods or not, as
needed. At minimum check_valid_frame and parse_frame needs to be
overridden.
GstElementClass |
the parent class |
| Optional. Called when the element starts processing. Allows opening external resources. | |
| Optional. Called when the element stops processing. Allows closing external resources. | |
| allows the subclass to be notified of the actual caps set. | |
| Check if the given piece of data contains a valid frame. | |
| Parse the already checked frame. Subclass need to set the buffer timestamp, duration, caps and possibly other necessary metadata. This is called with srcpad's STREAM_LOCK held. | |
| Optional. Called just prior to pushing a frame (after any pending events have been sent) to give subclass a chance to perform additional actions at this time (e.g. tag sending) or to decide whether this buffer should be dropped or not (e.g. custom segment clipping). | |
| Optional. Convert between formats. | |
| Optional. Event handler on the sink pad. This function should return TRUE if the event was handled and can be dropped. | |
| Optional. Event handler on the source pad. Should return TRUE if the event was handled and can be dropped. | |
| allows the subclass to do its own sink get caps if needed. Since: 0.10.36 | |
| Optional. Called until it doesn't return GST_FLOW_OK anymore for the first buffers. Can be used by the subclass to detect the stream format. Since: 0.10.36 |
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.
|
GstBaseParse. |
|
GstFormat. |
|
duration value. |
|
how often to update the duration estimate based on bitrate, or 0. |
Since 0.10.33
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()).
|
GstBaseParse. |
|
average bitrate in bits/second |
Since 0.10.33
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.
|
GstBaseParse. |
|
Minimum size of the data that this base class should give to subclass. |
Since 0.10.33
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.
|
a GstBaseParse |
|
TRUE if parser should run in passthrough mode |
Since 0.10.33
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.
|
a GstBaseParse |
|
set if frame starts can be identified |
Since 0.10.33
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.
|
a GstBaseParse |
|
whether frames carry timing information |
Since 0.10.33
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.
|
the GstBaseParse to set |
|
frames per second (numerator). |
|
frames per second (denominator). |
|
frames needed before a segment for subsequent decode |
|
frames needed after a segment |
Since 0.10.33
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.
|
GstBaseParse. |
|
GstFormat describing the source format. |
|
Source value to be converted. |
|
GstFormat defining the converted format. |
|
Pointer where the conversion result will be put. |
Returns : |
TRUE if conversion was successful. |
Since 0.10.33
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.
|
GstBaseParse. |
|
offset of entry |
|
timestamp associated with offset |
|
whether entry refers to keyframe |
|
add entry disregarding sanity checks |
Returns : |
gboolean indicating whether entry was added |
Since 0.10.33
typedef struct {
GstBuffer * buffer;
guint flags;
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.
GstBuffer * |
data to check for valid frame or parsed frame. Subclass is allowed to replace this buffer. |
guint |
a combination of input and output GstBaseParseFrameFlags that convey additional context to subclass or allow subclass to tune subsequent GstBaseParse actions. |
gint |
subclass can set this to indicates the metadata overhead for the given frame, which is then used to enable more accurate bitrate computations. If this is -1, it is assumed that this frame should be skipped in bitrate calculation. |
Since 0.10.33
typedef enum {
GST_BASE_PARSE_FRAME_FLAG_NONE = 0,
GST_BASE_PARSE_FRAME_FLAG_NO_FRAME = (1 << 0),
GST_BASE_PARSE_FRAME_FLAG_CLIP = (1 << 1)
} GstBaseParseFrameFlags;
Flags to be used in a GstBaseParseFrame.
| no flag | |
| set to indicate this buffer should not be counted as frame, e.g. if this frame is dependent on a previous one. As it is not counted as a frame, bitrate increases but frame to time conversions are maintained. | |
pre_push_frame can set this to indicate
that regular segment clipping can still be performed (as opposed to
any custom one having been done).
|
Since 0.10.33
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.
|
a GstBuffer. [transfer none] |
|
the flags |
|
number of bytes in this frame which should be counted as metadata overhead, ie. not used to calculate the average bitrate. Set to -1 to mark the entire frame as metadata. If in doubt, set to 0. |
Returns : |
a newly-allocated GstBaseParseFrame. Free with
gst_base_parse_frame_free() when no longer needed, unless you gave
away ownership to gst_base_parse_push_frame(). |
Since 0.10.33
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.
|
GstBaseParseFrame. |
Since 0.10.33
GstFlowReturn gst_base_parse_push_frame (GstBaseParse *parse,GstBaseParseFrame *frame);
Pushes the frame downstream, sends any pending events and
does some timestamp and segment handling. Takes ownership
of frame and will clear it (if it was initialised with
gst_base_parse_frame_init()) or free it.
This must be called with sinkpad STREAM_LOCK held.
|
GstBaseParse. |
|
a GstBaseParseFrame. [transfer full] |
Returns : |
GstFlowReturn |
Since 0.10.33
#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)
|
base parse instance |
Since 0.10.33
#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.
Since 0.10.33
#define GST_BASE_PARSE_FLOW_QUEUED GST_FLOW_CUSTOM_SUCCESS_1
A GstFlowReturn that can be returned from parse frame to indicate that the buffer will be queued to be pushed when the next OK
Since 0.10.33
#define GST_BASE_PARSE_LOST_SYNC(parse) (!!(GST_BASE_PARSE_CAST(parse)->flags & GST_BASE_PARSE_FLAG_LOST_SYNC))
Obtains current sync status.
|
base parse instance |
Since 0.10.33
#define GST_BASE_PARSE_SINK_PAD(obj) (GST_BASE_PARSE_CAST (obj)->sinkpad)
Gives the pointer to the sink GstPad object of the element.
|
base parse instance |
Since 0.10.33
#define GST_BASE_PARSE_SRC_PAD(obj) (GST_BASE_PARSE_CAST (obj)->srcpad)
Gives the pointer to the source GstPad object of the element.
|
base parse instance |
Since 0.10.33