GstVideoEncoder

GstVideoEncoder — Base class for video encoders

Functions

Types and Values

Object Hierarchy


Description

This base class is for video encoders turning raw video into encoded video data.

GstVideoEncoder and subclass should cooperate as follows.

  1. Configuration

    • Initially, GstVideoEncoder calls start when the encoder element is activated, which allows subclass to perform any global setup.

    • GstVideoEncoder calls set_format to inform subclass of the format of input video data that it is about to receive. Subclass should setup for encoding and configure base class as appropriate (e.g. latency). While unlikely, it might be called more than once, if changing input parameters require reconfiguration. Baseclass will ensure that processing of current configuration is finished.

    • GstVideoEncoder calls stop at end of all processing.

  2. Data processing

    • Base class collects input data and metadata into a frame and hands this to subclass' handle_frame.

    • If codec processing results in encoded data, subclass should call gst_video_encoder_finish_frame to have encoded data pushed downstream.

    • If implemented, baseclass calls subclass pre_push just prior to pushing to allow subclasses to modify some metadata on the buffer. If it returns GST_FLOW_OK, the buffer is pushed downstream.

    • GstVideoEncoderClass will handle both srcpad and sinkpad events. Sink events will be passed to subclass if event callback has been provided.

  3. Shutdown phase

    • GstVideoEncoder 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 should also be able to provide fixed src pad caps in getcaps by the time it calls gst_video_encoder_finish_frame .

Things that subclass need to take care of:

  • Provide pad templates

  • Provide source pad caps before pushing the first buffer

  • Accept data in handle_frame and provide encoded results to gst_video_encoder_finish_frame.

Functions

GST_VIDEO_ENCODER_CAST()

#define GST_VIDEO_ENCODER_CAST(enc) ((GstVideoEncoder*)enc)

GST_VIDEO_ENCODER_SINK_PAD()

#define GST_VIDEO_ENCODER_SINK_PAD(obj)        (((GstVideoEncoder *) (obj))->sinkpad)

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

Parameters

obj

a GstVideoEncoder

 

GST_VIDEO_ENCODER_SRC_PAD()

#define GST_VIDEO_ENCODER_SRC_PAD(obj)         (((GstVideoEncoder *) (obj))->srcpad)

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

Parameters

obj

a GstVideoEncoder

 

GST_VIDEO_ENCODER_INPUT_SEGMENT()

#define GST_VIDEO_ENCODER_INPUT_SEGMENT(obj)     (GST_VIDEO_ENCODER_CAST (obj)->input_segment)

Gives the segment of the element.

Parameters

obj

base parse instance

 

GST_VIDEO_ENCODER_OUTPUT_SEGMENT()

#define GST_VIDEO_ENCODER_OUTPUT_SEGMENT(obj)     (GST_VIDEO_ENCODER_CAST (obj)->output_segment)

Gives the segment of the element.

Parameters

obj

base parse instance

 

GST_VIDEO_ENCODER_STREAM_LOCK()

#define GST_VIDEO_ENCODER_STREAM_LOCK(encoder) g_rec_mutex_lock (&GST_VIDEO_ENCODER (encoder)->stream_lock)

Obtain a lock to protect the encoder function from concurrent access.

Parameters

encoder

video encoder instance

 

GST_VIDEO_ENCODER_STREAM_UNLOCK()

#define GST_VIDEO_ENCODER_STREAM_UNLOCK(encoder) g_rec_mutex_unlock (&GST_VIDEO_ENCODER (encoder)->stream_lock)

Release the lock that protects the encoder function from concurrent access.

Parameters

encoder

video encoder instance

 

gst_video_encoder_allocate_output_buffer ()

GstBuffer *
gst_video_encoder_allocate_output_buffer
                               (GstVideoEncoder *encoder,
                                gsize size);

Helper function that allocates a buffer to hold an encoded video frame for encoder 's current GstVideoCodecState.

Parameters

encoder

a GstVideoEncoder

 

size

size of the buffer

 

Returns

allocated buffer.

[transfer full]


gst_video_encoder_allocate_output_frame ()

GstFlowReturn
gst_video_encoder_allocate_output_frame
                               (GstVideoEncoder *encoder,
                                GstVideoCodecFrame *frame,
                                gsize size);

Helper function that allocates a buffer to hold an encoded video frame for encoder 's current GstVideoCodecState. Subclass should already have configured video state and set src pad caps.

The buffer allocated here is owned by the frame and you should only keep references to the frame, not the buffer.

Parameters

encoder

a GstVideoEncoder

 

frame

a GstVideoCodecFrame

 

size

size of the buffer

 

Returns

GST_FLOW_OK if an output buffer could be allocated


gst_video_encoder_get_allocator ()

void
gst_video_encoder_get_allocator (GstVideoEncoder *encoder,
                                 GstAllocator **allocator,
                                 GstAllocationParams *params);

Lets GstVideoEncoder sub-classes to know the memory allocator used by the base class and its params .

Unref the allocator after use it.

Parameters

encoder

a GstVideoEncoder

 

allocator

the GstAllocator used.

[out][allow-none][transfer full]

params

the GstAllocatorParams of allocator .

[out][allow-none][transfer full]

gst_video_encoder_finish_frame ()

GstFlowReturn
gst_video_encoder_finish_frame (GstVideoEncoder *encoder,
                                GstVideoCodecFrame *frame);

frame must have a valid encoded data buffer, whose metadata fields are then appropriately set according to frame data or no buffer at all if the frame should be dropped. It is subsequently pushed downstream or provided to pre_push . In any case, the frame is considered finished and released.

After calling this function the output buffer of the frame is to be considered read-only. This function will also change the metadata of the buffer.

Parameters

encoder

a GstVideoEncoder

 

frame

an encoded GstVideoCodecFrame.

[transfer full]

Returns

a GstFlowReturn resulting from sending data downstream


gst_video_encoder_negotiate ()

gboolean
gst_video_encoder_negotiate (GstVideoEncoder *encoder);

Negotiate with downstream elements to currently configured GstVideoCodecState. Unmark GST_PAD_FLAG_NEED_RECONFIGURE in any case. But mark it again if negotiate fails.

Parameters

encoder

a GstVideoEncoder

 

Returns

TRUE if the negotiation succeeded, else FALSE.


gst_video_encoder_get_frame ()

GstVideoCodecFrame *
gst_video_encoder_get_frame (GstVideoEncoder *encoder,
                             int frame_number);

Get a pending unfinished GstVideoCodecFrame

Parameters

encoder

a GstVideoEnccoder

 

frame_number

system_frame_number of a frame

 

Returns

pending unfinished GstVideoCodecFrame identified by frame_number .

[transfer full]


gst_video_encoder_get_frames ()

GList *
gst_video_encoder_get_frames (GstVideoEncoder *encoder);

Get all pending unfinished GstVideoCodecFrame

Parameters

encoder

a GstVideoEncoder

 

Returns

pending unfinished GstVideoCodecFrame.

[transfer full][element-type GstVideoCodecFrame]


gst_video_encoder_get_oldest_frame ()

GstVideoCodecFrame *
gst_video_encoder_get_oldest_frame (GstVideoEncoder *encoder);

Get the oldest unfinished pending GstVideoCodecFrame

Parameters

encoder

a GstVideoEncoder

 

Returns

oldest unfinished pending GstVideoCodecFrame.

[transfer full]


gst_video_encoder_set_headers ()

void
gst_video_encoder_set_headers (GstVideoEncoder *encoder,
                               GList *headers);

Set the codec headers to be sent downstream whenever requested.

Parameters

encoder

a GstVideoEncoder

 

headers

a list of GstBuffer containing the codec header.

[transfer full][element-type GstBuffer]

gst_video_encoder_get_latency ()

void
gst_video_encoder_get_latency (GstVideoEncoder *encoder,
                               GstClockTime *min_latency,
                               GstClockTime *max_latency);

Query the configured encoding latency. Results will be returned via min_latency and max_latency .

Parameters

encoder

a GstVideoEncoder

 

min_latency

address of variable in which to store the configured minimum latency, or NULL.

[out][allow-none]

max_latency

address of variable in which to store the configured maximum latency, or NULL.

[out][allow-none]

gst_video_encoder_set_latency ()

void
gst_video_encoder_set_latency (GstVideoEncoder *encoder,
                               GstClockTime min_latency,
                               GstClockTime max_latency);

Informs baseclass of encoding latency.

Parameters

encoder

a GstVideoEncoder

 

min_latency

minimum latency

 

max_latency

maximum latency

 

gst_video_encoder_set_output_state ()

GstVideoCodecState *
gst_video_encoder_set_output_state (GstVideoEncoder *encoder,
                                    GstCaps *caps,
                                    GstVideoCodecState *reference);

Creates a new GstVideoCodecState with the specified caps as the output state for the encoder. Any previously set output state on encoder will be replaced by the newly created one.

The specified caps should not contain any resolution, pixel-aspect-ratio, framerate, codec-data, .... Those should be specified instead in the returned GstVideoCodecState.

If the subclass wishes to copy over existing fields (like pixel aspect ratio, or framerate) from an existing GstVideoCodecState, it can be provided as a reference .

If the subclass wishes to override some fields from the output state (like pixel-aspect-ratio or framerate) it can do so on the returned GstVideoCodecState.

The new output state will only take effect (set on pads and buffers) starting from the next call to gst_video_encoder_finish_frame().

Parameters

encoder

a GstVideoEncoder

 

caps

the GstCaps to use for the output.

[transfer full]

reference

An optional reference GstVideoCodecState .

[allow-none][transfer none]

Returns

the newly configured output state.

[transfer full]


gst_video_encoder_get_output_state ()

GstVideoCodecState *
gst_video_encoder_get_output_state (GstVideoEncoder *encoder);

Get the current GstVideoCodecState

Parameters

encoder

a GstVideoEncoder

 

Returns

GstVideoCodecState describing format of video data.

[transfer full]


gst_video_encoder_proxy_getcaps ()

GstCaps *
gst_video_encoder_proxy_getcaps (GstVideoEncoder *enc,
                                 GstCaps *caps,
                                 GstCaps *filter);

Returns caps that express caps (or sink template caps if caps == NULL) restricted to resolution/format/... combinations supported by downstream elements (e.g. muxers).

Parameters

enc

a GstVideoEncoder

 

caps

initial caps

 

filter

filter caps

 

Returns

a GstCaps owned by caller


gst_video_encoder_merge_tags ()

void
gst_video_encoder_merge_tags (GstVideoEncoder *encoder,
                              const GstTagList *tags,
                              GstTagMergeMode mode);

Adds tags to so-called pending tags, which will be processed before pushing out data downstream.

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.

MT safe.

Parameters

encoder

a GstVideoEncoder

 

tags

a GstTagList to merge

 

mode

the GstTagMergeMode to use

 

Types and Values

GST_VIDEO_ENCODER_FLOW_DROPPED

#define GST_VIDEO_ENCODER_FLOW_DROPPED GST_FLOW_CUSTOM_SUCCESS_1

Returned when the event/buffer should be dropped.


GST_VIDEO_ENCODER_FLOW_NEED_DATA

#define GST_VIDEO_ENCODER_FLOW_NEED_DATA GST_FLOW_CUSTOM_SUCCESS

Returned while parsing to indicate more data is needed.


GST_VIDEO_ENCODER_SINK_NAME

#define GST_VIDEO_ENCODER_SINK_NAME    "sink"

The name of the templates for the sink pad.


GST_VIDEO_ENCODER_SRC_NAME

#define GST_VIDEO_ENCODER_SRC_NAME     "src"

The name of the templates for the source pad.


struct GstVideoEncoder

struct GstVideoEncoder {
};

The opaque GstVideoEncoder data structure.


struct GstVideoEncoderClass

struct GstVideoEncoderClass {
  /* virtual methods for subclasses */
  gboolean      (*open)         (GstVideoEncoder *encoder);

  gboolean      (*close)        (GstVideoEncoder *encoder);

  gboolean      (*start)        (GstVideoEncoder *encoder);

  gboolean      (*stop)         (GstVideoEncoder *encoder);

  gboolean      (*set_format)   (GstVideoEncoder *encoder,
				 GstVideoCodecState *state);

  GstFlowReturn (*handle_frame) (GstVideoEncoder *encoder,
				 GstVideoCodecFrame *frame);

  gboolean      (*reset)        (GstVideoEncoder *encoder,
				 gboolean hard);

  GstFlowReturn (*finish)       (GstVideoEncoder *encoder);

  GstFlowReturn (*pre_push)     (GstVideoEncoder *encoder,
				 GstVideoCodecFrame *frame);

  GstCaps *     (*getcaps)      (GstVideoEncoder *enc,
                                 GstCaps *filter);

  gboolean      (*sink_event)   (GstVideoEncoder *encoder,
				 GstEvent *event);

  gboolean      (*src_event)    (GstVideoEncoder *encoder,
				 GstEvent *event);

  gboolean      (*negotiate)    (GstVideoEncoder *encoder);

  gboolean      (*decide_allocation)  (GstVideoEncoder *encoder, GstQuery *query);

  gboolean      (*propose_allocation) (GstVideoEncoder * encoder,
                                       GstQuery * query);
  gboolean      (*flush)              (GstVideoEncoder *encoder);

  gboolean      (*sink_query)     (GstVideoEncoder *encoder,
				   GstQuery *query);

  gboolean      (*src_query)      (GstVideoEncoder *encoder,
				   GstQuery *query);
};

Subclasses can override any of the available virtual methods or not, as needed. At minimum handle_frame needs to be overridden, and set_format and get_caps are likely needed as well.

Members

open ()

Optional. Called when the element changes to GST_STATE_READY. Allows opening external resources.

 

close ()

Optional. Called when the element changes to GST_STATE_NULL. Allows closing external resources.

 

start ()

Optional. Called when the element starts processing. Allows opening external resources.

 

stop ()

Optional. Called when the element stops processing. Allows closing external resources.

 

set_format ()

Optional. Notifies subclass of incoming data format. GstVideoCodecState fields have already been set according to provided caps.

 

handle_frame ()

Provides input frame to subclass.

 

reset ()

Optional. Allows subclass (encoder) to perform post-seek semantics reset. Deprecated.

 

finish ()

Optional. Called to request subclass to dispatch any pending remaining data (e.g. at EOS).

 

pre_push ()

Optional. Allows subclass to push frame downstream in whatever shape or form it deems appropriate. If not provided, provided encoded frame data is simply pushed downstream.

 

getcaps ()

Optional. Allows for a custom sink getcaps implementation (e.g. for multichannel input specification). If not implemented, default returns gst_video_encoder_proxy_getcaps applied to sink template caps.

 

sink_event ()

Optional. Event handler on the sink pad. This function should return TRUE if the event was handled and should be discarded (i.e. not unref'ed). Subclasses should chain up to the parent implementation to invoke the default handler.

 

src_event ()

Optional. Event handler on the source pad. This function should return TRUE if the event was handled and should be discarded (i.e. not unref'ed). Subclasses should chain up to the parent implementation to invoke the default handler.

 

negotiate ()

Optional. Negotiate with downstream and configure buffer pools, etc. Subclasses should chain up to the parent implementation to invoke the default handler.

 

decide_allocation ()

Optional. Setup the allocation parameters for allocating output buffers. The passed in query contains the result of the downstream allocation query. Subclasses should chain up to the parent implementation to invoke the default handler.

 

propose_allocation ()

Optional. Propose buffer allocation parameters for upstream elements. Subclasses should chain up to the parent implementation to invoke the default handler.

 

flush ()

Optional. Flush all remaining data from the encoder without pushing it downstream. Since: 1.2

 

sink_query ()

Optional. Query handler on the sink pad. This function should return TRUE if the query could be performed. Subclasses should chain up to the parent implementation to invoke the default handler. Since 1.4

 

src_query ()

Optional. Query handler on the source pad. This function should return TRUE if the query could be performed. Subclasses should chain up to the parent implementation to invoke the default handler. Since 1.4