gstaudioencoder

gstaudioencoder — Base class for audio encoders

Functions

Properties

gboolean hard-resync Read / Write
gboolean mark-granule Read
gboolean perfect-timestamp Read / Write
gint64 tolerance Read / Write

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstAudioEncoder

Implemented Interfaces

GstAudioEncoder implements GstPreset.

Includes

#include <gst/audio/gstaudioencoder.h>

Description

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

GstAudioEncoder and subclass should cooperate as follows.

  1. Configuration

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

    • GstAudioEncoder calls set_format to inform subclass of the format of input audio data that it is about to receive. Subclass should setup for encoding and configure various base class parameters appropriately, notably those directing desired input data handling. While unlikely, it might be called more than once, if changing input parameters require reconfiguration.

    • GstAudioEncoder calls stop at end of all processing.

  2. Data processing

    • Base class gathers input sample data (as directed by the context's frame_samples and frame_max) and provides this to subclass' handle_frame.

    • If codec processing results in encoded data, subclass should call gst_audio_encoder_finish_frame() to have encoded data pushed downstream. Alternatively, it might also call gst_audio_encoder_finish_frame() (with a NULL buffer and some number of dropped samples) to indicate dropped (non-encoded) samples.

    • Just prior to actually pushing a buffer downstream, it is passed to pre_push.

    • During the parsing process GstAudioEncoderClass will handle both srcpad and sinkpad events. Sink events will be passed to subclass if event callback has been provided.

  3. Shutdown phase

    • GstAudioEncoder 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. This is typically when base class calls subclass' set_format function, though it might be delayed until calling gst_audio_encoder_finish_frame .

In summary, above process should have subclass concentrating on codec data processing while leaving other matters to base class, such as most notably timestamp handling. While it may exert more control in this area (see e.g. pre_push ), it is very much not recommended.

In particular, base class will either favor tracking upstream timestamps (at the possible expense of jitter) or aim to arrange for a perfect stream of output timestamps, depending on “perfect-timestamp”. However, in the latter case, the input may not be so perfect or ideal, which is handled as follows. An input timestamp is compared with the expected timestamp as dictated by input sample stream and if the deviation is less than “tolerance”, the deviation is discarded. Otherwise, it is considered a discontuinity and subsequent output timestamp is resynced to the new position after performing configured discontinuity processing. In the non-perfect-timestamp case, an upstream variation exceeding tolerance only leads to marking DISCONT on subsequent outgoing (while timestamps are adjusted to upstream regardless of variation). While DISCONT is also marked in the perfect-timestamp case, this one optionally (see “hard-resync”) performs some additional steps, such as clipping of (early) input samples or draining all currently remaining input data, depending on the direction of the discontuinity.

If perfect timestamps are arranged, it is also possible to request baseclass (usually set by subclass) to provide additional buffer metadata (in OFFSET and OFFSET_END) fields according to granule defined semantics currently needed by oggmux. Specifically, OFFSET is set to granulepos (= sample count including buffer) and OFFSET_END to corresponding timestamp (as determined by same sample count and sample rate).

Things that subclass need to take care of:

  • Provide pad templates

  • Set source pad caps when appropriate

  • Inform base class of buffer processing needs using context's frame_samples and frame_bytes.

  • Set user-configurable properties to sane defaults for format and implementing codec at hand, e.g. those controlling timestamp behaviour and discontinuity processing.

  • Accept data in handle_frame and provide encoded results to gst_audio_encoder_finish_frame().

Functions

GST_AUDIO_ENCODER_SINK_PAD()

#define GST_AUDIO_ENCODER_SINK_PAD(obj) (GST_AUDIO_ENCODER_CAST (obj)->sinkpad)

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

Parameters

obj

audio encoder instance

 

GST_AUDIO_ENCODER_SRC_PAD()

#define GST_AUDIO_ENCODER_SRC_PAD(obj) (GST_AUDIO_ENCODER_CAST (obj)->srcpad)

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

Parameters

obj

audio encoder instance

 

gst_audio_encoder_finish_frame ()

GstFlowReturn
gst_audio_encoder_finish_frame (GstAudioEncoder *enc,
                                GstBuffer *buffer,
                                gint samples);

Collects encoded data and pushes encoded data downstream. Source pad caps must be set when this is called.

If samples < 0, then best estimate is all samples provided to encoder (subclass) so far. buf may be NULL, in which case next number of samples are considered discarded, e.g. as a result of discontinuous transmission, and a discontinuity is marked.

Note that samples received in gst_audio_encoder_handle_frame() may be invalidated by a call to this function.

Parameters

enc

a GstAudioEncoder

 

buffer

encoded data

 

samples

number of samples (per channel) represented by encoded data

 

Returns

a GstFlowReturn that should be escalated to caller (of caller)


gst_audio_encoder_allocate_output_buffer ()

GstBuffer *
gst_audio_encoder_allocate_output_buffer
                               (GstAudioEncoder *enc,
                                gsize size);

Helper function that allocates a buffer to hold an encoded audio frame for enc 's current output format.

Parameters

enc

a GstAudioEncoder

 

size

size of the buffer

 

Returns

allocated buffer.

[transfer full]


gst_audio_encoder_get_allocator ()

void
gst_audio_encoder_get_allocator (GstAudioEncoder *enc,
                                 GstAllocator **allocator,
                                 GstAllocationParams *params);

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

Unref the allocator after use it.

Parameters

enc

a GstAudioEncoder

 

allocator

the GstAllocator used.

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

params

the GstAllocatorParams of allocator .

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

gst_audio_encoder_set_output_format ()

gboolean
gst_audio_encoder_set_output_format (GstAudioEncoder *enc,
                                     GstCaps *caps);

gst_audio_encoder_negotiate ()

gboolean
gst_audio_encoder_negotiate (GstAudioEncoder *enc);

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

Parameters

enc

a GstAudioEncoder

 

Returns

TRUE if the negotiation succeeded, else FALSE.


gst_audio_encoder_get_audio_info ()

GstAudioInfo *
gst_audio_encoder_get_audio_info (GstAudioEncoder *enc);

Parameters

enc

a GstAudioEncoder

 

Returns

a GstAudioInfo describing the input audio format


gst_audio_encoder_get_drainable ()

gboolean
gst_audio_encoder_get_drainable (GstAudioEncoder *enc);

Queries encoder drain handling.

Parameters

enc

a GstAudioEncoder

 

Returns

TRUE if drainable handling is enabled.

MT safe.


gst_audio_encoder_get_frame_max ()

gint
gst_audio_encoder_get_frame_max (GstAudioEncoder *enc);

Parameters

enc

a GstAudioEncoder

 

Returns

currently configured maximum handled frames


gst_audio_encoder_get_frame_samples_min ()

gint
gst_audio_encoder_get_frame_samples_min
                               (GstAudioEncoder *enc);

Parameters

enc

a GstAudioEncoder

 

Returns

currently minimum requested samples per frame


gst_audio_encoder_get_frame_samples_max ()

gint
gst_audio_encoder_get_frame_samples_max
                               (GstAudioEncoder *enc);

Parameters

enc

a GstAudioEncoder

 

Returns

currently maximum requested samples per frame


gst_audio_encoder_get_hard_min ()

gboolean
gst_audio_encoder_get_hard_min (GstAudioEncoder *enc);

Queries encoder hard minimum handling.

Parameters

enc

a GstAudioEncoder

 

Returns

TRUE if hard minimum handling is enabled.

MT safe.


gst_audio_encoder_get_hard_resync ()

gboolean
gst_audio_encoder_get_hard_resync (GstAudioEncoder *enc);

gst_audio_encoder_get_latency ()

void
gst_audio_encoder_get_latency (GstAudioEncoder *enc,
                               GstClockTime *min,
                               GstClockTime *max);

Sets the variables pointed to by min and max to the currently configured latency.

Parameters

enc

a GstAudioEncoder

 

min

a pointer to storage to hold minimum latency.

[out][allow-none]

max

a pointer to storage to hold maximum latency.

[out][allow-none]

gst_audio_encoder_get_lookahead ()

gint
gst_audio_encoder_get_lookahead (GstAudioEncoder *enc);

Parameters

enc

a GstAudioEncoder

 

Returns

currently configured encoder lookahead


gst_audio_encoder_get_mark_granule ()

gboolean
gst_audio_encoder_get_mark_granule (GstAudioEncoder *enc);

Queries if the encoder will handle granule marking.

Parameters

enc

a GstAudioEncoder

 

Returns

TRUE if granule marking is enabled.

MT safe.


gst_audio_encoder_get_perfect_timestamp ()

gboolean
gst_audio_encoder_get_perfect_timestamp
                               (GstAudioEncoder *enc);

Queries encoder perfect timestamp behaviour.

Parameters

enc

a GstAudioEncoder

 

Returns

TRUE if perfect timestamp setting enabled.

MT safe.


gst_audio_encoder_get_tolerance ()

GstClockTime
gst_audio_encoder_get_tolerance (GstAudioEncoder *enc);

Queries current audio jitter tolerance threshold.

Parameters

enc

a GstAudioEncoder

 

Returns

encoder audio jitter tolerance threshold.

MT safe.


gst_audio_encoder_proxy_getcaps ()

GstCaps *
gst_audio_encoder_proxy_getcaps (GstAudioEncoder *enc,
                                 GstCaps *caps,
                                 GstCaps *filter);

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

Parameters

enc

a GstAudioEncoder

 

caps

initial caps

 

filter

filter caps

 

Returns

a GstCaps owned by caller


gst_audio_encoder_set_drainable ()

void
gst_audio_encoder_set_drainable (GstAudioEncoder *enc,
                                 gboolean enabled);

Configures encoder drain handling. If drainable, subclass might be handed a NULL buffer to have it return any leftover encoded data. Otherwise, it is not considered so capable and will only ever be passed real data.

MT safe.

Parameters

enc

a GstAudioEncoder

 

enabled

new state

 

gst_audio_encoder_set_frame_max ()

void
gst_audio_encoder_set_frame_max (GstAudioEncoder *enc,
                                 gint num);

Sets max number of frames accepted at once (assumed minimally 1). Requires frame_samples_min and frame_samples_max to be the equal.

Parameters

enc

a GstAudioEncoder

 

num

number of frames

 

gst_audio_encoder_set_frame_samples_min ()

void
gst_audio_encoder_set_frame_samples_min
                               (GstAudioEncoder *enc,
                                gint num);

Sets number of samples (per channel) subclass needs to be handed, at least or will be handed all available if 0.

If an exact number of samples is required, gst_audio_encoder_set_frame_samples_max() must be called with the same number.

Parameters

enc

a GstAudioEncoder

 

num

number of samples per frame

 

gst_audio_encoder_set_frame_samples_max ()

void
gst_audio_encoder_set_frame_samples_max
                               (GstAudioEncoder *enc,
                                gint num);

Sets number of samples (per channel) subclass needs to be handed, at most or will be handed all available if 0.

If an exact number of samples is required, gst_audio_encoder_set_frame_samples_min() must be called with the same number.

Parameters

enc

a GstAudioEncoder

 

num

number of samples per frame

 

gst_audio_encoder_set_hard_min ()

void
gst_audio_encoder_set_hard_min (GstAudioEncoder *enc,
                                gboolean enabled);

Configures encoder hard minimum handling. If enabled, subclass will never be handed less samples than it configured, which otherwise might occur near end-of-data handling. Instead, the leftover samples will simply be discarded.

MT safe.

Parameters

enc

a GstAudioEncoder

 

enabled

new state

 

gst_audio_encoder_set_hard_resync ()

void
gst_audio_encoder_set_hard_resync (GstAudioEncoder *enc,
                                   gboolean enabled);

gst_audio_encoder_set_headers ()

void
gst_audio_encoder_set_headers (GstAudioEncoder *enc,
                               GList *headers);

Set the codec headers to be sent downstream whenever requested.

Parameters

enc

a GstAudioEncoder

 

headers

a list of GstBuffer containing the codec header.

[transfer full][element-type Gst.Buffer]

gst_audio_encoder_set_latency ()

void
gst_audio_encoder_set_latency (GstAudioEncoder *enc,
                               GstClockTime min,
                               GstClockTime max);

Sets encoder latency.

Parameters

enc

a GstAudioEncoder

 

min

minimum latency

 

max

maximum latency

 

gst_audio_encoder_set_lookahead ()

void
gst_audio_encoder_set_lookahead (GstAudioEncoder *enc,
                                 gint num);

Sets encoder lookahead (in units of input rate samples)

Parameters

enc

a GstAudioEncoder

 

num

lookahead

 

gst_audio_encoder_set_mark_granule ()

void
gst_audio_encoder_set_mark_granule (GstAudioEncoder *enc,
                                    gboolean enabled);

Enable or disable encoder granule handling.

MT safe.

Parameters

enc

a GstAudioEncoder

 

enabled

new state

 

gst_audio_encoder_set_perfect_timestamp ()

void
gst_audio_encoder_set_perfect_timestamp
                               (GstAudioEncoder *enc,
                                gboolean enabled);

Enable or disable encoder perfect output timestamp preference.

MT safe.

Parameters

enc

a GstAudioEncoder

 

enabled

new state

 

gst_audio_encoder_set_tolerance ()

void
gst_audio_encoder_set_tolerance (GstAudioEncoder *enc,
                                 GstClockTime tolerance);

Configures encoder audio jitter tolerance threshold.

MT safe.

Parameters

enc

a GstAudioEncoder

 

tolerance

new tolerance

 

gst_audio_encoder_merge_tags ()

void
gst_audio_encoder_merge_tags (GstAudioEncoder *enc,
                              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, although it should be aware that baseclass already takes care of the usual CODEC/AUDIO_CODEC tags.

MT safe.

Parameters

enc

a GstAudioEncoder

 

tags

a GstTagList to merge

 

mode

the GstTagMergeMode to use

 

Types and Values

struct GstAudioEncoder

struct GstAudioEncoder;

The opaque GstAudioEncoder data structure.


struct GstAudioEncoderClass

struct GstAudioEncoderClass {
  GstElementClass element_class;

  /* virtual methods for subclasses */

  gboolean      (*start)              (GstAudioEncoder *enc);

  gboolean      (*stop)               (GstAudioEncoder *enc);

  gboolean      (*set_format)         (GstAudioEncoder *enc,
                                       GstAudioInfo        *info);

  GstFlowReturn (*handle_frame)       (GstAudioEncoder *enc,
                                       GstBuffer *buffer);

  void          (*flush)              (GstAudioEncoder *enc);

  GstFlowReturn (*pre_push)           (GstAudioEncoder *enc,
                                       GstBuffer **buffer);

  gboolean      (*sink_event)         (GstAudioEncoder *enc,
                                       GstEvent *event);

  gboolean      (*src_event)          (GstAudioEncoder *enc,
                                       GstEvent *event);

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

  gboolean      (*open)               (GstAudioEncoder *enc);

  gboolean      (*close)              (GstAudioEncoder *enc);

  gboolean      (*negotiate)          (GstAudioEncoder *enc);

  gboolean      (*decide_allocation)  (GstAudioEncoder *enc, GstQuery *query);

  gboolean      (*propose_allocation) (GstAudioEncoder * enc,
                                       GstQuery * query);
};

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

Members

GstElementClass element_class;

The parent class structure

 

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 ()

Notifies subclass of incoming data format. GstAudioInfo contains the format according to provided caps.

 

handle_frame ()

Provides input samples (or NULL to clear any remaining data) according to directions as configured by the subclass using the API. Input data ref management is performed by base class, subclass should not care or intervene, and input data is only valid until next call to base class, most notably a call to gst_audio_encoder_finish_frame().

 

flush ()

Optional. Instructs subclass to clear any codec caches and discard any pending samples and not yet returned encoded data.

 

pre_push ()

Optional. Called just prior to pushing (encoded data) buffer downstream. Subclass has full discretionary access to buffer, and a not OK flow return will abort downstream pushing.

 

sink_event ()

Optional. Event handler on the sink pad. Subclasses should chain up to the parent implementation to invoke the default handler.

 

src_event ()

Optional. Event handler on the src pad. Subclasses should chain up to the parent implementation to invoke the default handler.

 

getcaps ()

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

 

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.

 

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_AUDIO_ENCODER_SINK_NAME

#define GST_AUDIO_ENCODER_SINK_NAME "sink"

the name of the templates for the sink pad


GST_AUDIO_ENCODER_SRC_NAME

#define GST_AUDIO_ENCODER_SRC_NAME	        "src"

the name of the templates for the source pad

Property Details

The “hard-resync” property

  “hard-resync”              gboolean

Perform clipping and sample flushing upon discontinuity.

Flags: Read / Write

Default value: FALSE


The “mark-granule” property

  “mark-granule”             gboolean

Apply granule semantics to buffer metadata (implies perfect-timestamp).

Flags: Read

Default value: FALSE


The “perfect-timestamp” property

  “perfect-timestamp”        gboolean

Favour perfect timestamps over tracking upstream timestamps.

Flags: Read / Write

Default value: FALSE


The “tolerance” property

  “tolerance”                gint64

Consider discontinuity if timestamp jitter/imperfection exceeds tolerance (ns).

Flags: Read / Write

Allowed values: >= 0

Default value: 40000000

See Also

GstBaseTransform