GstVideoEncoder

GstVideoEncoder — Base class for video encoders

Synopsis

#define             GST_VIDEO_ENCODER_CAST              (enc)
#define             GST_VIDEO_ENCODER_FLOW_DROPPED
#define             GST_VIDEO_ENCODER_FLOW_NEED_DATA
#define             GST_VIDEO_ENCODER_SINK_NAME
#define             GST_VIDEO_ENCODER_SINK_PAD          (obj)
#define             GST_VIDEO_ENCODER_SRC_NAME
#define             GST_VIDEO_ENCODER_SRC_PAD           (obj)
#define             GST_VIDEO_ENCODER_INPUT_SEGMENT     (obj)
#define             GST_VIDEO_ENCODER_OUTPUT_SEGMENT    (obj)
#define             GST_VIDEO_ENCODER_STREAM_LOCK       (encoder)
#define             GST_VIDEO_ENCODER_STREAM_UNLOCK     (encoder)
struct              GstVideoEncoder;
struct              GstVideoEncoderClass;
GstBuffer *         gst_video_encoder_allocate_output_buffer
                                                        (GstVideoEncoder *encoder,
                                                         gsize size);
GstFlowReturn       gst_video_encoder_allocate_output_frame
                                                        (GstVideoEncoder *encoder,
                                                         GstVideoCodecFrame *frame,
                                                         gsize size);
void                gst_video_encoder_get_allocator     (GstVideoEncoder *encoder,
                                                         GstAllocator **allocator,
                                                         GstAllocationParams *params);
GstFlowReturn       gst_video_encoder_finish_frame      (GstVideoEncoder *encoder,
                                                         GstVideoCodecFrame *frame);
gboolean            gst_video_encoder_negotiate         (GstVideoEncoder *encoder);
GstVideoCodecFrame * gst_video_encoder_get_frame        (GstVideoEncoder *encoder,
                                                         int frame_number);
GList *             gst_video_encoder_get_frames        (GstVideoEncoder *encoder);
GstVideoCodecFrame * gst_video_encoder_get_oldest_frame (GstVideoEncoder *encoder);
void                gst_video_encoder_set_headers       (GstVideoEncoder *encoder,
                                                         GList *headers);
void                gst_video_encoder_get_latency       (GstVideoEncoder *encoder,
                                                         GstClockTime *min_latency,
                                                         GstClockTime *max_latency);
void                gst_video_encoder_set_latency       (GstVideoEncoder *encoder,
                                                         GstClockTime min_latency,
                                                         GstClockTime max_latency);
gboolean            gst_video_encoder_get_discont       (GstVideoEncoder *encoder);
void                gst_video_encoder_set_discont       (GstVideoEncoder *encoder);
GstVideoCodecState * gst_video_encoder_set_output_state (GstVideoEncoder *encoder,
                                                         GstCaps *caps,
                                                         GstVideoCodecState *reference);
GstVideoCodecState * gst_video_encoder_get_output_state (GstVideoEncoder *encoder);
GstCaps *           gst_video_encoder_proxy_getcaps     (GstVideoEncoder *enc,
                                                         GstCaps *caps,
                                                         GstCaps *filter);
void                gst_video_encoder_merge_tags        (GstVideoEncoder *encoder,
                                                         const GstTagList *tags,
                                                         GstTagMergeMode mode);

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.

Details

GST_VIDEO_ENCODER_CAST()

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

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_SINK_PAD()

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

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

obj :

a GstVideoEncoder

GST_VIDEO_ENCODER_SRC_NAME

#define GST_VIDEO_ENCODER_SRC_NAME     "src"

The name of the templates for the source pad.


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.

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.

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.

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.

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.

encoder :

video encoder instance

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);
};

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

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.

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.

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.

encoder :

a GstVideoEncoder

min_latency :

minimum latency

max_latency :

maximum latency

gst_video_encoder_get_discont ()

gboolean            gst_video_encoder_get_discont       (GstVideoEncoder *encoder);

gst_video_encoder_set_discont ()

void                gst_video_encoder_set_discont       (GstVideoEncoder *encoder);

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().

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

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).

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.

encoder :

a GstVideoEncoder

tags :

a GstTagList to merge

mode :

the GstTagMergeMode to use