WebM Codec SDK

Files | Data Structures | Macros | Typedefs | Enumerations | Functions
Encoder Algorithm Interface
Common Algorithm Interface

## Files
file | vpx_encoder.h
| Describes the encoder algorithm interface to applications.

## Data Structures
struct | vpx_fixed_buf
| Generic fixed size buffer structure. More...
struct | vpx_codec_cx_pkt
| Encoder output packet. More...
struct | vpx_codec_enc_output_cx_cb_pair
| Callback function pointer / user data pair storage. More...
struct | vpx_rational
| Rational Number. More...
struct | vpx_codec_enc_cfg
| Encoder configuration structure. More...
struct | vpx_svc_parameters
| vp9 svc extra configure parameters More...

## Macros
#define | VPX_TS_MAX_PERIODICITY 16
#define | VPX_TS_MAX_LAYERS 5
#define | VPX_MAX_LAYERS 12
#define | VPX_SS_MAX_LAYERS 5
#define | VPX_SS_DEFAULT_LAYERS 1
#define | VPX_ENCODER_ABI_VERSION
| Current ABI version number.
#define | VPX_CODEC_CAP_PSNR 0x10000
| Encoder capabilities bitfield.
#define | VPX_CODEC_CAP_OUTPUT_PARTITION 0x20000
#define | VPX_CODEC_USE_PSNR 0x10000
| Initialization-time Feature Enabling.
#define | VPX_CODEC_USE_OUTPUT_PARTITION 0x20000
| Make the encoder output one partition at a time.
#define | VPX_CODEC_USE_HIGHBITDEPTH 0x40000
#define | VPX_FRAME_IS_KEY 0x1u
#define | VPX_FRAME_IS_DROPPABLE 0x2u
| frame can be dropped without affecting the stream (no future frame depends on this one)
#define | VPX_FRAME_IS_INVISIBLE 0x4u
| frame should be decoded but will not be shown
#define | VPX_FRAME_IS_FRAGMENT 0x8u
| this is a fragment of the encoded frame
#define | VPX_ERROR_RESILIENT_DEFAULT 0x1u
| Improve resiliency against losses of whole frames.
#define | VPX_ERROR_RESILIENT_PARTITIONS 0x2u
| The frame partitions are independently decodable by the bool decoder, meaning that partitions can be decoded even though earlier partitions have been lost. Note that intra prediction is still done over the partition boundary.
#define | VPX_EFLAG_FORCE_KF (1 << 0)
#define | VPX_EFLAG_CALCULATE_PSNR (1 << 1)
#define | vpx_codec_enc_init(ctx, iface, cfg, flags)
| Convenience macro for vpx_codec_enc_init_ver().
#define | vpx_codec_enc_init_multi(ctx, iface, cfg, num_enc, flags, dsf)
| Convenience macro for vpx_codec_enc_init_multi_ver().
#define | VPX_DL_REALTIME 1ul
| deadline parameter analogous to VPx REALTIME mode.
#define | VPX_DL_GOOD_QUALITY 1000000ul
| deadline parameter analogous to VPx GOOD QUALITY mode.
#define | VPX_DL_BEST_QUALITY 0ul
| deadline parameter analogous to VPx BEST QUALITY mode.

## Typedefs
typedef struct vpx_fixed_buf | vpx_fixed_buf_t
| Generic fixed size buffer structure.
typedef int64_t | vpx_codec_pts_t
| Time Stamp Type.
typedef uint32_t | vpx_codec_frame_flags_t
| Compressed Frame Flags.
typedef uint32_t | vpx_codec_er_flags_t
| Error Resilient flags.
typedef struct vpx_codec_cx_pkt | vpx_codec_cx_pkt_t
| Encoder output packet.
typedef void(* | vpx_codec_enc_output_cx_pkt_cb_fn_t) (vpx_codec_cx_pkt_t *pkt, void *user_data)
| Encoder return output buffer callback.
typedef struct vpx_codec_enc_output_cx_cb_pair | vpx_codec_priv_output_cx_pkt_cb_pair_t
| Callback function pointer / user data pair storage.
typedef struct vpx_rational | vpx_rational_t
| Rational Number.
typedef enum vpx_enc_pass | vpx_enc_pass
| Multi-pass Encoding Pass.
typedef long | vpx_enc_frame_flags_t
| Encoded Frame Flags.
typedef struct vpx_codec_enc_cfg | vpx_codec_enc_cfg_t
| Encoder configuration structure.
typedef struct vpx_svc_parameters | vpx_svc_extra_cfg_t
| vp9 svc extra configure parameters
typedef unsigned long | vpx_enc_deadline_t
| Encode Deadline.

## Enumerations
enum | vpx_codec_cx_pkt_kind { VPX_CODEC_CX_FRAME_PKT , VPX_CODEC_STATS_PKT , VPX_CODEC_FPMB_STATS_PKT , VPX_CODEC_PSNR_PKT , VPX_CODEC_CUSTOM_PKT = 256 }
| Encoder output packet variants. More...
enum | vpx_enc_pass { VPX_RC_ONE_PASS , VPX_RC_FIRST_PASS , VPX_RC_LAST_PASS }
| Multi-pass Encoding Pass. More...
enum | vpx_rc_mode { VPX_VBR , VPX_CBR , VPX_CQ , VPX_Q }
| Rate control mode. More...
enum | vpx_kf_mode { VPX_KF_FIXED , VPX_KF_AUTO , VPX_KF_DISABLED = 0 }
| Keyframe placement mode. More...

## Functions
vpx_codec_err_t | vpx_codec_enc_init_ver (vpx_codec_ctx_t *ctx, vpx_codec_iface_t *iface, const vpx_codec_enc_cfg_t *cfg, vpx_codec_flags_t flags, int ver)
| Initialize an encoder instance.
vpx_codec_err_t | vpx_codec_enc_init_multi_ver (vpx_codec_ctx_t *ctx, vpx_codec_iface_t *iface, const vpx_codec_enc_cfg_t *cfg, int num_enc, vpx_codec_flags_t flags, const vpx_rational_t *dsf, int ver)
| Initialize multi-encoder instance.
vpx_codec_err_t | vpx_codec_enc_config_default (vpx_codec_iface_t *iface, vpx_codec_enc_cfg_t *cfg, unsigned int usage)
| Get a default configuration.
vpx_codec_err_t | vpx_codec_enc_config_set (vpx_codec_ctx_t *ctx, const vpx_codec_enc_cfg_t *cfg)
| Set or change configuration.
vpx_fixed_buf_t * | vpx_codec_get_global_headers (vpx_codec_ctx_t *ctx)
| Get global stream headers.
vpx_codec_err_t | vpx_codec_encode (vpx_codec_ctx_t *ctx, const vpx_image_t *img, vpx_codec_pts_t pts, unsigned long duration, vpx_enc_frame_flags_t flags, vpx_enc_deadline_t deadline)
| Encode a frame.
vpx_codec_err_t | vpx_codec_set_cx_data_buf (vpx_codec_ctx_t *ctx, const vpx_fixed_buf_t *buf, unsigned int pad_before, unsigned int pad_after)
| Set compressed data output buffer.
const vpx_codec_cx_pkt_t * | vpx_codec_get_cx_data (vpx_codec_ctx_t *ctx, vpx_codec_iter_t *iter)
| Encoded data iterator.
const vpx_image_t * | vpx_codec_get_preview_frame (vpx_codec_ctx_t *ctx)
| Get Preview Frame.

## Detailed Description

This abstraction allows applications using this encoder to easily support multiple video formats with minimal code duplication. This section describes the interface common to all encoders.

## Macro Definition Documentation

## ◆ VPX_TS_MAX_PERIODICITY

#define VPX_TS_MAX_PERIODICITY 16

Temporal Scalability: Maximum length of the sequence defining frame layer membership

## ◆ VPX_TS_MAX_LAYERS

#define VPX_TS_MAX_LAYERS 5

Temporal Scalability: Maximum number of coding layers

## ◆ VPX_MAX_LAYERS

#define VPX_MAX_LAYERS 12

Temporal+Spatial Scalability: Maximum number of coding layers

## ◆ VPX_SS_MAX_LAYERS

#define VPX_SS_MAX_LAYERS 5

Spatial Scalability: Maximum number of coding layers

## ◆ VPX_SS_DEFAULT_LAYERS

#define VPX_SS_DEFAULT_LAYERS 1

Spatial Scalability: Default number of coding layers

## ◆ VPX_CODEC_CAP_PSNR

#define VPX_CODEC_CAP_PSNR 0x10000

Encoder capabilities bitfield.

Each encoder advertises the capabilities it supports as part of its vpx_codec_iface_t interface structure. Capabilities are extra interfaces or functionality, and are not required to be supported by an encoder.

The available flags are specified by VPX_CODEC_CAP_* defines. Can issue PSNR packets

## ◆ VPX_CODEC_CAP_OUTPUT_PARTITION

#define VPX_CODEC_CAP_OUTPUT_PARTITION 0x20000

Can output one partition at a time. Each partition is returned in its own VPX_CODEC_CX_FRAME_PKT, with the FRAME_IS_FRAGMENT flag set for every partition but the last. In this mode all frames are always returned partition by partition.

## ◆ VPX_CODEC_USE_PSNR

#define VPX_CODEC_USE_PSNR 0x10000

Initialization-time Feature Enabling.

Certain codec features must be known at initialization time, to allow for proper memory allocation.

The available flags are specified by VPX_CODEC_USE_* defines. Calculate PSNR on each frame

## ◆ VPX_CODEC_USE_HIGHBITDEPTH

#define VPX_CODEC_USE_HIGHBITDEPTH 0x40000

Use high bitdepth

## ◆ VPX_FRAME_IS_KEY

#define VPX_FRAME_IS_KEY 0x1u

frame is the start of a GOP

## ◆ VPX_ERROR_RESILIENT_PARTITIONS

#define VPX_ERROR_RESILIENT_PARTITIONS 0x2u

The frame partitions are independently decodable by the bool decoder, meaning that partitions can be decoded even though earlier partitions have been lost. Note that intra prediction is still done over the partition boundary.

Note
  This is only supported by VP8.

## ◆ VPX_EFLAG_FORCE_KF

#define VPX_EFLAG_FORCE_KF (1 << 0)

Force this frame to be a keyframe

## ◆ VPX_EFLAG_CALCULATE_PSNR

#define VPX_EFLAG_CALCULATE_PSNR (1 << 1)

Calculate PSNR on this frame, requires g_lag_in_frames to be 0

## ◆ vpx_codec_enc_init

#define vpx_codec_enc_init | ( |  | ctx,
|  |  | iface,
|  |  | cfg,
|  |  | flags )

Value:
vpx_codec_enc_init_ver(ctx, iface, cfg, flags, VPX_ENCODER_ABI_VERSION)
vpx_codec_enc_init_ver
vpx_codec_err_t vpx_codec_enc_init_ver(vpx_codec_ctx_t *ctx, vpx_codec_iface_t *iface, const vpx_codec_enc_cfg_t *cfg, vpx_codec_flags_t flags, int ver)
Initialize an encoder instance.
VPX_ENCODER_ABI_VERSION
#define VPX_ENCODER_ABI_VERSION
Current ABI version number.
Definition vpx_encoder.h:65

Convenience macro for vpx_codec_enc_init_ver().

Ensures the ABI version parameter is properly set.

## ◆ vpx_codec_enc_init_multi

#define vpx_codec_enc_init_multi | ( |  | ctx,
|  |  | iface,
|  |  | cfg,
|  |  | num_enc,
|  |  | flags,
|  |  | dsf )

Value:
vpx_codec_enc_init_multi_ver(ctx, iface, cfg, num_enc, flags, dsf, \
VPX_ENCODER_ABI_VERSION)
vpx_codec_enc_init_multi_ver
vpx_codec_err_t vpx_codec_enc_init_multi_ver(vpx_codec_ctx_t *ctx, vpx_codec_iface_t *iface, const vpx_codec_enc_cfg_t *cfg, int num_enc, vpx_codec_flags_t flags, const vpx_rational_t *dsf, int ver)
Initialize multi-encoder instance.

Convenience macro for vpx_codec_enc_init_multi_ver().

Ensures the ABI version parameter is properly set.

## Typedef Documentation

## ◆ vpx_fixed_buf_t

typedef struct vpx_fixed_buf vpx_fixed_buf_t

Generic fixed size buffer structure.

This structure is able to hold a reference to any fixed size buffer. alias for struct vpx_fixed_buf

## ◆ vpx_codec_pts_t

typedef int64_t vpx_codec_pts_t

Time Stamp Type.

An integer, which when multiplied by the stream's time base, provides the absolute time of a sample.

## ◆ vpx_codec_frame_flags_t

typedef uint32_t vpx_codec_frame_flags_t

Compressed Frame Flags.

This type represents a bitfield containing information about a compressed frame that may be useful to an application. The most significant 16 bits can be used by an algorithm to provide additional detail, for example to support frame types that are codec specific (MPEG-1 D-frames for example)

## ◆ vpx_codec_er_flags_t

typedef uint32_t vpx_codec_er_flags_t

Error Resilient flags.

These flags define which error resilient features to enable in the encoder. The flags are specified through the vpx_codec_enc_cfg::g_error_resilient variable.

## ◆ vpx_codec_cx_pkt_t

typedef struct vpx_codec_cx_pkt vpx_codec_cx_pkt_t

Encoder output packet.

This structure contains the different kinds of output data the encoder may produce while compressing a frame. alias for struct vpx_codec_cx_pkt

## ◆ vpx_codec_enc_output_cx_pkt_cb_fn_t

typedef void(* vpx_codec_enc_output_cx_pkt_cb_fn_t) (vpx_codec_cx_pkt_t *pkt, void *user_data)

Encoder return output buffer callback.

This callback function, when registered, returns with packets when each spatial layer is encoded.

## ◆ vpx_rational_t

typedef struct vpx_rational vpx_rational_t

Rational Number.

This structure holds a fractional value. alias for struct vpx_rational

## ◆ vpx_enc_frame_flags_t

typedef long vpx_enc_frame_flags_t

Encoded Frame Flags.

This type indicates a bitfield to be passed to vpx_codec_encode(), defining per-frame boolean values. By convention, bits common to all codecs will be named VPX_EFLAG_*, and bits specific to an algorithm will be named /algo/_eflag_*. The lower order 16 bits are reserved for common use.

## ◆ vpx_codec_enc_cfg_t

typedef struct vpx_codec_enc_cfg vpx_codec_enc_cfg_t

Encoder configuration structure.

This structure contains the encoder settings that have common representations across all codecs. This doesn't imply that all codecs support all features, however. alias for struct vpx_codec_enc_cfg

## ◆ vpx_svc_extra_cfg_t

typedef struct vpx_svc_parameters vpx_svc_extra_cfg_t

vp9 svc extra configure parameters

This defines max/min quantizers and scale factors for each layer

## ◆ vpx_enc_deadline_t

typedef unsigned long vpx_enc_deadline_t

Encode Deadline.

This type indicates a deadline, in microseconds, to be passed to vpx_codec_encode().

## Enumeration Type Documentation

## ◆ vpx_codec_cx_pkt_kind

enum vpx_codec_cx_pkt_kind

Encoder output packet variants.

This enumeration lists the different kinds of data packets that can be returned by calls to vpx_codec_get_cx_data(). Algorithms MAY extend this list to provide additional functionality.

Enumerator
VPX_CODEC_CX_FRAME_PKT | Compressed video frame
VPX_CODEC_STATS_PKT | Two-pass statistics for this frame
VPX_CODEC_FPMB_STATS_PKT | first pass mb statistics for this frame
VPX_CODEC_PSNR_PKT | PSNR statistics for this frame
VPX_CODEC_CUSTOM_PKT | Algorithm extensions

## ◆ vpx_enc_pass

enum vpx_enc_pass

Multi-pass Encoding Pass.

Enumerator
VPX_RC_ONE_PASS | Single pass mode
VPX_RC_FIRST_PASS | First pass of multi-pass mode
VPX_RC_LAST_PASS | Final pass of multi-pass mode

## ◆ vpx_rc_mode

enum vpx_rc_mode

Rate control mode.

Enumerator
VPX_VBR | Variable Bit Rate (VBR) mode
VPX_CBR | Constant Bit Rate (CBR) mode
VPX_CQ | Constrained Quality (CQ) mode
VPX_Q | Constant Quality (Q) mode

## ◆ vpx_kf_mode

enum vpx_kf_mode

Keyframe placement mode.

This enumeration determines whether keyframes are placed automatically by the encoder or whether this behavior is disabled. Older releases of this SDK were implemented such that VPX_KF_FIXED meant keyframes were disabled. This name is confusing for this behavior, so the new symbols to be used are VPX_KF_AUTO and VPX_KF_DISABLED.

Enumerator
VPX_KF_FIXED | deprecated, implies VPX_KF_DISABLED
VPX_KF_AUTO | Encoder determines optimal placement automatically
VPX_KF_DISABLED | Encoder does not place keyframes.

## Function Documentation

## ◆ vpx_codec_enc_init_ver()

vpx_codec_err_t vpx_codec_enc_init_ver | ( | vpx_codec_ctx_t * | ctx,
|  | vpx_codec_iface_t * | iface,
|  | const vpx_codec_enc_cfg_t * | cfg,
|  | vpx_codec_flags_t | flags,
|  | int | ver )

Initialize an encoder instance.

Initializes an encoder context using the given interface. Applications should call the vpx_codec_enc_init convenience macro instead of this function directly, to ensure that the ABI version number parameter is properly initialized.

If the library was configured with –disable-multithread, this call is not thread safe and should be guarded with a lock if being used in a multithreaded context.

If vpx_codec_enc_init_ver() fails, it is not necessary to call vpx_codec_destroy() on the encoder context.

Parameters

  [in] | ctx | Pointer to this instance's context.
  [in] | iface | Pointer to the algorithm interface to use.
  [in] | cfg | Configuration to use.
  [in] | flags | Bitfield of VPX_CODEC_USE_* flags
  [in] | ver | ABI version number. Must be set to VPX_ENCODER_ABI_VERSION

Return values

  VPX_CODEC_OK | The decoder algorithm initialized.
  VPX_CODEC_MEM_ERROR | Memory allocation failed.

## ◆ vpx_codec_enc_init_multi_ver()

vpx_codec_err_t vpx_codec_enc_init_multi_ver | ( | vpx_codec_ctx_t * | ctx,
|  | vpx_codec_iface_t * | iface,
|  | const vpx_codec_enc_cfg_t * | cfg,
|  | int | num_enc,
|  | vpx_codec_flags_t | flags,
|  | const vpx_rational_t * | dsf,
|  | int | ver )

Initialize multi-encoder instance.

Initializes multiple encoder contexts using the given interface. Applications should call the vpx_codec_enc_init_multi convenience macro instead of this function directly, to ensure that the ABI version number parameter is properly initialized.

Parameters

  [in] | ctx | Pointer to an array of num_enc instances' contexts.
  [in] | iface | Pointer to the algorithm interface to use.
  [in] | cfg | An array of num_enc configurations to use.
  [in] | num_enc | Total number of encoders.
  [in] | flags | Bitfield of VPX_CODEC_USE_* flags
  [in] | dsf | Pointer to an array of num_enc down-sampling factors.
  [in] | ver | ABI version number. Must be set to VPX_ENCODER_ABI_VERSION

Return values

  VPX_CODEC_OK | The encoder algorithm has been initialized.
  VPX_CODEC_MEM_ERROR | Memory allocation failed.

Note
  This is only supported by VP8. iface must point to the interface to the VP8 encoder.

## ◆ vpx_codec_enc_config_default()

vpx_codec_err_t vpx_codec_enc_config_default | ( | vpx_codec_iface_t * | iface,
|  | vpx_codec_enc_cfg_t * | cfg,
|  | unsigned int | usage )

Get a default configuration.

Initializes a encoder configuration structure with default values. Supports the notion of "usages" so that an algorithm may offer different default settings depending on the user's intended goal. This function SHOULD be called by all applications to initialize the configuration structure before specializing the configuration with application specific values.

Parameters

  [in] | iface | Pointer to the algorithm interface to use.
  [out] | cfg | Configuration buffer to populate.
  [in] | usage | Must be set to 0.

Return values

  VPX_CODEC_OK | The configuration was populated.
  VPX_CODEC_INCAPABLE | Interface is not an encoder interface.
  VPX_CODEC_INVALID_PARAM | A parameter was NULL, or the usage value was not recognized.

## ◆ vpx_codec_enc_config_set()

vpx_codec_err_t vpx_codec_enc_config_set | ( | vpx_codec_ctx_t * | ctx,
|  | const vpx_codec_enc_cfg_t * | cfg )

Set or change configuration.

Reconfigures an encoder instance according to the given configuration.

Parameters

  [in] | ctx | Pointer to this instance's context
  [in] | cfg | Configuration buffer to use

Return values

  VPX_CODEC_OK | The configuration was populated.
  VPX_CODEC_INCAPABLE | Interface is not an encoder interface.
  VPX_CODEC_INVALID_PARAM | A parameter was NULL, or the usage value was not recognized.

## ◆ vpx_codec_get_global_headers()

vpx_fixed_buf_t * vpx_codec_get_global_headers | ( | vpx_codec_ctx_t * | ctx | ) |

Get global stream headers.

Retrieves a stream level global header packet, if supported by the codec.

- VP8: Unsupported
- VP9: Returns a buffer of ID (1 byte)|Length (1 byte)|Length bytes values. The function should be called after encoding to retrieve the most accurate information.

Parameters

  [in] | ctx | Pointer to this instance's context

Return values

  NULL | Encoder does not support global header
  Non-NULL | Pointer to buffer containing global header packet. The buffer pointer and its contents are only valid for the lifetime of ctx. The contents may change in subsequent calls to the function.

See also
  https://www.webmproject.org/docs/container/#vp9-codec-feature-metadata-codecprivate

## ◆ vpx_codec_encode()

vpx_codec_err_t vpx_codec_encode | ( | vpx_codec_ctx_t * | ctx,
|  | const vpx_image_t * | img,
|  | vpx_codec_pts_t | pts,
|  | unsigned long | duration,
|  | vpx_enc_frame_flags_t | flags,
|  | vpx_enc_deadline_t | deadline )

Encode a frame.

Encodes a video frame at the given "presentation time." The presentation time stamp (PTS) MUST be strictly increasing.

The encoder supports the notion of a soft real-time deadline. Given a non-zero value to the deadline parameter, the encoder will make a "best effort" guarantee to return before the given time slice expires. It is implicit that limiting the available time to encode will degrade the output quality. The encoder can be given an unlimited time to produce the best possible frame by specifying a deadline of '0'. This deadline supersedes the VPx notion of "best quality, good quality, realtime". Applications that wish to map these former settings to the new deadline based system can use the symbols VPX_DL_REALTIME, VPX_DL_GOOD_QUALITY, and VPX_DL_BEST_QUALITY.

When the last frame has been passed to the encoder, this function should continue to be called, with the img parameter set to NULL. This will signal the end-of-stream condition to the encoder and allow it to encode any held buffers. Encoding is complete when vpx_codec_encode() is called and vpx_codec_get_cx_data() returns no data.

Parameters

  [in] | ctx | Pointer to this instance's context
  [in] | img | Image data to encode, NULL to flush. Encoding sample values outside the range [0..(1<<img->bit_depth)-1] is undefined behavior.
  [in] | pts | Presentation time stamp, in timebase units.
  [in] | duration | Duration to show frame, in timebase units.
  [in] | flags | Flags to use for encoding this frame.
  [in] | deadline | Time to spend encoding, in microseconds. (0=infinite)

Return values

  VPX_CODEC_OK | The configuration was populated.
  VPX_CODEC_INCAPABLE | Interface is not an encoder interface.
  VPX_CODEC_INVALID_PARAM | A parameter was NULL, the image format is unsupported, etc.

## ◆ vpx_codec_set_cx_data_buf()

vpx_codec_err_t vpx_codec_set_cx_data_buf | ( | vpx_codec_ctx_t * | ctx,
|  | const vpx_fixed_buf_t * | buf,
|  | unsigned int | pad_before,
|  | unsigned int | pad_after )

Set compressed data output buffer.

Sets the buffer that the codec should output the compressed data into. This call effectively sets the buffer pointer returned in the next VPX_CODEC_CX_FRAME_PKT packet. Subsequent packets will be appended into this buffer. The buffer is preserved across frames, so applications must periodically call this function after flushing the accumulated compressed data to disk or to the network to reset the pointer to the buffer's head.

pad_before bytes will be skipped before writing the compressed data, and pad_after bytes will be appended to the packet. The size of the packet will be the sum of the size of the actual compressed data, pad_before, and pad_after. The padding bytes will be preserved (not overwritten).

Note that calling this function does not guarantee that the returned compressed data will be placed into the specified buffer. In the event that the encoded data will not fit into the buffer provided, the returned packet MAY point to an internal buffer, as it would if this call were never used. In this event, the output packet will NOT have any padding, and the application must free space and copy it to the proper place. This is of particular note in configurations that may output multiple packets for a single encoded frame (e.g., lagged encoding) or if the application does not reset the buffer periodically.

Applications may restore the default behavior of the codec providing the compressed data buffer by calling this function with a NULL buffer.

Applications MUST NOT call this function during iteration of vpx_codec_get_cx_data().

Parameters

  [in] | ctx | Pointer to this instance's context
  [in] | buf | Buffer to store compressed data into
  [in] | pad_before | Bytes to skip before writing compressed data
  [in] | pad_after | Bytes to skip after writing compressed data

Return values

  VPX_CODEC_OK | The buffer was set successfully.
  VPX_CODEC_INVALID_PARAM | A parameter was NULL, the image format is unsupported, etc.

Note
  duration and deadline are of the unsigned long type, which can be 32 or 64 bits. duration and deadline must be less than or equal to UINT32_MAX so that their ranges are independent of the size of unsigned long.

## ◆ vpx_codec_get_cx_data()

const vpx_codec_cx_pkt_t * vpx_codec_get_cx_data | ( | vpx_codec_ctx_t * | ctx,
|  | vpx_codec_iter_t * | iter )

Encoded data iterator.

Iterates over a list of data packets to be passed from the encoder to the application. The different kinds of packets available are enumerated in vpx_codec_cx_pkt_kind.

VPX_CODEC_CX_FRAME_PKT packets should be passed to the application's muxer. Multiple compressed frames may be in the list. VPX_CODEC_STATS_PKT packets should be appended to a global buffer.

The application MUST silently ignore any packet kinds that it does not recognize or support.

The data buffers returned from this function are only guaranteed to be valid until the application makes another call to any vpx_codec_* function.

Parameters

  [in] | ctx | Pointer to this instance's context
  [in,out] | iter | Iterator storage, initialized to NULL

Returns
  Returns a pointer to an output data packet (compressed frame data, two-pass statistics, etc.) or NULL to signal end-of-list.

## ◆ vpx_codec_get_preview_frame()

const vpx_image_t * vpx_codec_get_preview_frame | ( | vpx_codec_ctx_t * | ctx | ) |

Get Preview Frame.

Returns an image that can be used as a preview. Shows the image as it would exist at the decompressor. The application MUST NOT write into this image buffer.

Parameters

  [in] | ctx | Pointer to this instance's context

Returns
  Returns a pointer to a preview image, or NULL if no image is available.