FFmpeg之HWContextType

HWContextType算是ffmpeg中为硬解码第三方接口的一个辅助类，它自己有两个辅助子类 AVHWDeviceContext和AVHWFramesContext。 AVHWDeviceContext主要表示硬件上下文 AVHWFramesContext主要表示硬件Frame的一些参数，比如你解码后的YUV数据还在硬件上，那么就通过这个类去存储相关参数。

那么它辅助硬解码器做什么呢？我们还是通过英伟达的例子来看

const HWContextType ff_hwcontext_type_cuda = { .type = AV_HWDEVICE_TYPE_CUDA, .name = "CUDA", .device_hwctx_size = sizeof(AVCUDADeviceContext), .frames_priv_size = sizeof(CUDAFramesContext), .device_create = cuda_device_create, .device_derive = cuda_device_derive, .device_init = cuda_device_init, .device_uninit = cuda_device_uninit, .frames_get_constraints = cuda_frames_get_constraints, .frames_init = cuda_frames_init, .frames_get_buffer = cuda_get_buffer, .transfer_get_formats = cuda_transfer_get_formats, .transfer_data_to = cuda_transfer_data, .transfer_data_from = cuda_transfer_data, .pix_fmts = (const enum AVPixelFormat[]){ AV_PIX_FMT_CUDA, AV_PIX_FMT_NONE }, };

仔细看上面函数就发现，全部是device mem操作，大白话说就是ffmpeg通过这套机制来实现D2H或者H2D的操作，别无其它。

具体看看结构体定义吧，一大堆函数指针，这些就是你要实现的，不一定全部要实现，实现你自己想要的就可以了，主要的有transfer_data_to/transfer_data_from，map_to/map_from。

typedef struct HWContextType { enum AVHWDeviceType type; const char *name; /** * An array of pixel formats supported by the AVHWFramesContext instances * Terminated by AV_PIX_FMT_NONE. */ const enum AVPixelFormat *pix_fmts; /** * size of the public hardware-specific context, * i.e. AVHWDeviceContext.hwctx */ size_t device_hwctx_size; /** * size of the private data, i.e. * AVHWDeviceInternal.priv */ size_t device_priv_size; /** * Size of the hardware-specific device configuration. * (Used to query hwframe constraints.) */ size_t device_hwconfig_size; /** * size of the public frame pool hardware-specific context, * i.e. AVHWFramesContext.hwctx */ size_t frames_hwctx_size; /** * size of the private data, i.e. * AVHWFramesInternal.priv */ size_t frames_priv_size; int (*device_create)(AVHWDeviceContext *ctx, const char *device, AVDictionary *opts, int flags); int (*device_derive)(AVHWDeviceContext *dst_ctx, AVHWDeviceContext *src_ctx, AVDictionary *opts, int flags); int (*device_init)(AVHWDeviceContext *ctx); void (*device_uninit)(AVHWDeviceContext *ctx); int (*frames_get_constraints)(AVHWDeviceContext *ctx, const void *hwconfig, AVHWFramesConstraints *constraints); int (*frames_init)(AVHWFramesContext *ctx); void (*frames_uninit)(AVHWFramesContext *ctx); int (*frames_get_buffer)(AVHWFramesContext *ctx, AVFrame *frame); int (*transfer_get_formats)(AVHWFramesContext *ctx, enum AVHWFrameTransferDirection dir, enum AVPixelFormat **formats); int (*transfer_data_to)(AVHWFramesContext *ctx, AVFrame *dst, const AVFrame *src); int (*transfer_data_from)(AVHWFramesContext *ctx, AVFrame *dst, const AVFrame *src); int (*map_to)(AVHWFramesContext *ctx, AVFrame *dst, const AVFrame *src, int flags); int (*map_from)(AVHWFramesContext *ctx, AVFrame *dst, const AVFrame *src, int flags); int (*frames_derive_to)(AVHWFramesContext *dst_ctx, AVHWFramesContext *src_ctx, int flags); int (*frames_derive_from)(AVHWFramesContext *dst_ctx, AVHWFramesContext *src_ctx, int flags); } HWContextType;

AVHWFramesContext结构体表示

/** * This struct describes a set or pool of "hardware" frames (i.e. those with * data not located in normal system memory). All the frames in the pool are * assumed to be allocated in the same way and interchangeable. * * This struct is reference-counted with the AVBuffer mechanism and tied to a * given AVHWDeviceContext instance. The av_hwframe_ctx_alloc() constructor * yields a reference, whose data field points to the actual AVHWFramesContext * struct. */ typedef struct AVHWFramesContext { /** * A class for logging. */ const AVClass *av_class; /** * Private data used internally by libavutil. Must not be accessed in any * way by the caller. */ AVHWFramesInternal *internal; /** * A reference to the parent AVHWDeviceContext. This reference is owned and * managed by the enclosing AVHWFramesContext, but the caller may derive * additional references from it. */ AVBufferRef *device_ref; /** * The parent AVHWDeviceContext. This is simply a pointer to * device_ref->data provided for convenience. * * Set by libavutil in av_hwframe_ctx_init(). */ AVHWDeviceContext *device_ctx; /** * The format-specific data, allocated and freed automatically along with * this context. * * Should be cast by the user to the format-specific context defined in the * corresponding header (hwframe_*.h) and filled as described in the * documentation before calling av_hwframe_ctx_init(). * * After any frames using this context are created, the contents of this * struct should not be modified by the caller. */ void *hwctx; /** * This field may be set by the caller before calling av_hwframe_ctx_init(). * * If non-NULL, this callback will be called when the last reference to * this context is unreferenced, immediately before it is freed. */ void (*free)(struct AVHWFramesContext *ctx); /** * Arbitrary user data, to be used e.g. by the free() callback. */ void *user_opaque; /** * A pool from which the frames are allocated by av_hwframe_get_buffer(). * This field may be set by the caller before calling av_hwframe_ctx_init(). * The buffers returned by calling av_buffer_pool_get() on this pool must * have the properties described in the documentation in the corresponding hw * type's header (hwcontext_*.h). The pool will be freed strictly before * this struct's free() callback is invoked. * * This field may be NULL, then libavutil will attempt to allocate a pool * internally. Note that certain device types enforce pools allocated at * fixed size (frame count), which cannot be extended dynamically. In such a * case, initial_pool_size must be set appropriately. */ AVBufferPool *pool; /** * Initial size of the frame pool. If a device type does not support * dynamically resizing the pool, then this is also the maximum pool size. * * May be set by the caller before calling av_hwframe_ctx_init(). Must be * set if pool is NULL and the device type does not support dynamic pools. */ int initial_pool_size; /** * The pixel format identifying the underlying HW surface type. * * Must be a hwaccel format, i.e. the corresponding descriptor must have the * AV_PIX_FMT_FLAG_HWACCEL flag set. * * Must be set by the user before calling av_hwframe_ctx_init(). */ enum AVPixelFormat format; /** * The pixel format identifying the actual data layout of the hardware * frames. * * Must be set by the caller before calling av_hwframe_ctx_init(). * * @note when the underlying API does not provide the exact data layout, but * only the colorspace/bit depth, this field should be set to the fully * planar version of that format (e.g. for 8-bit 420 YUV it should be * AV_PIX_FMT_YUV420P, not AV_PIX_FMT_NV12 or anything else). */ enum AVPixelFormat sw_format; /** * The allocated dimensions of the frames in this pool. * * Must be set by the user before calling av_hwframe_ctx_init(). */ int width, height; } AVHWFramesContext;

AVHWDeviceContext的结构体表示，硬件的抽象

/** * This struct aggregates all the (hardware/vendor-specific) "high-level" state, * i.e. state that is not tied to a concrete processing configuration. * E.g., in an API that supports hardware-accelerated encoding and decoding, * this struct will (if possible) wrap the state that is common to both encoding * and decoding and from which specific instances of encoders or decoders can be * derived. * * This struct is reference-counted with the AVBuffer mechanism. The * av_hwdevice_ctx_alloc() constructor yields a reference, whose data field * points to the actual AVHWDeviceContext. Further objects derived from * AVHWDeviceContext (such as AVHWFramesContext, describing a frame pool with * specific properties) will hold an internal reference to it. After all the * references are released, the AVHWDeviceContext itself will be freed, * optionally invoking a user-specified callback for uninitializing the hardware * state. */ typedef struct AVHWDeviceContext { /** * A class for logging. Set by av_hwdevice_ctx_alloc(). */ const AVClass *av_class; /** * Private data used internally by libavutil. Must not be accessed in any * way by the caller. */ AVHWDeviceInternal *internal; /** * This field identifies the underlying API used for hardware access. * * This field is set when this struct is allocated and never changed * afterwards. */ enum AVHWDeviceType type; /** * The format-specific data, allocated and freed by libavutil along with * this context. * * Should be cast by the user to the format-specific context defined in the * corresponding header (hwcontext_*.h) and filled as described in the * documentation before calling av_hwdevice_ctx_init(). * * After calling av_hwdevice_ctx_init() this struct should not be modified * by the caller. */ void *hwctx; /** * This field may be set by the caller before calling av_hwdevice_ctx_init(). * * If non-NULL, this callback will be called when the last reference to * this context is unreferenced, immediately before it is freed. * * @note when other objects (e.g an AVHWFramesContext) are derived from this * struct, this callback will be invoked after all such child objects * are fully uninitialized and their respective destructors invoked. */ void (*free)(struct AVHWDeviceContext *ctx); /** * Arbitrary user data, to be used e.g. by the free() callback. */ void *user_opaque; } AVHWDeviceContext; 常用函数

这些函数其实挺重要的，因为都是用户函数，通过这些函数去从解码器硬件上获取到你要的数据，比如av_hwframe_transfer_data/av_hwframe_get_buffer，就是说你在ffmpeg中不要显示的调用你自己的cuMemD2H或者H2D的函数，ffmpeg已经给你预留好了接口了，用这些接口去获取更加简单。

/** * Look up an AVHWDeviceType by name. * * @param name String name of the device type (case-insensitive). * @return The type from enum AVHWDeviceType, or AV_HWDEVICE_TYPE_NONE if * not found. */ enum AVHWDeviceType av_hwdevice_find_type_by_name(const char *name); /** Get the string name of an AVHWDeviceType. * * @param type Type from enum AVHWDeviceType. * @return Pointer to a static string containing the name, or NULL if the type * is not valid. */ const char *av_hwdevice_get_type_name(enum AVHWDeviceType type); /** * Iterate over supported device types. * * @param type AV_HWDEVICE_TYPE_NONE initially, then the previous type * returned by this function in subsequent iterations. * @return The next usable device type from enum AVHWDeviceType, or * AV_HWDEVICE_TYPE_NONE if there are no more. */ enum AVHWDeviceType av_hwdevice_iterate_types(enum AVHWDeviceType prev); /** * Allocate an AVHWDeviceContext for a given hardware type. * * @param type the type of the hardware device to allocate. * @return a reference to the newly created AVHWDeviceContext on success or NULL * on failure. */ AVBufferRef *av_hwdevice_ctx_alloc(enum AVHWDeviceType type); /** * Finalize the device context before use. This function must be called after * the context is filled with all the required information and before it is * used in any way. * * @param ref a reference to the AVHWDeviceContext * @return 0 on success, a negative AVERROR code on failure */ int av_hwdevice_ctx_init(AVBufferRef *ref); /** * Open a device of the specified type and create an AVHWDeviceContext for it. * * This is a convenience function intended to cover the simple cases. Callers * who need to fine-tune device creation/management should open the device * manually and then wrap it in an AVHWDeviceContext using * av_hwdevice_ctx_alloc()/av_hwdevice_ctx_init(). * * The returned context is already initialized and ready for use, the caller * should not call av_hwdevice_ctx_init() on it. The user_opaque/free fields of * the created AVHWDeviceContext are set by this function and should not be * touched by the caller. * * @param device_ctx On success, a reference to the newly-created device context * will be written here. The reference is owned by the caller * and must be released with av_buffer_unref() when no longer * needed. On failure, NULL will be written to this pointer. * @param type The type of the device to create. * @param device A type-specific string identifying the device to open. * @param opts A dictionary of additional (type-specific) options to use in * opening the device. The dictionary remains owned by the caller. * @param flags currently unused * * @return 0 on success, a negative AVERROR code on failure. */ int av_hwdevice_ctx_create(AVBufferRef **device_ctx, enum AVHWDeviceType type, const char *device, AVDictionary *opts, int flags); /** * Create a new device of the specified type from an existing device. * * If the source device is a device of the target type or was originally * derived from such a device (possibly through one or more intermediate * devices of other types), then this will return a reference to the * existing device of the same type as is requested. * * Otherwise, it will attempt to derive a new device from the given source * device. If direct derivation to the new type is not implemented, it will * attempt the same derivation from each ancestor of the source device in * turn looking for an implemented derivation method. * * @param dst_ctx On success, a reference to the newly-created * AVHWDeviceContext. * @param type The type of the new device to create. * @param src_ctx A reference to an existing AVHWDeviceContext which will be * used to create the new device. * @param flags Currently unused; should be set to zero. * @return Zero on success, a negative AVERROR code on failure. */ int av_hwdevice_ctx_create_derived(AVBufferRef **dst_ctx, enum AVHWDeviceType type, AVBufferRef *src_ctx, int flags); /** * Create a new device of the specified type from an existing device. * * This function performs the same action as av_hwdevice_ctx_create_derived, * however, it is able to set options for the new device to be derived. * * @param dst_ctx On success, a reference to the newly-created * AVHWDeviceContext. * @param type The type of the new device to create. * @param src_ctx A reference to an existing AVHWDeviceContext which will be * used to create the new device. * @param options Options for the new device to create, same format as in * av_hwdevice_ctx_create. * @param flags Currently unused; should be set to zero. * @return Zero on success, a negative AVERROR code on failure. */ int av_hwdevice_ctx_create_derived_opts(AVBufferRef **dst_ctx, enum AVHWDeviceType type, AVBufferRef *src_ctx, AVDictionary *options, int flags); /** * Allocate an AVHWFramesContext tied to a given device context. * * @param device_ctx a reference to a AVHWDeviceContext. This function will make * a new reference for internal use, the one passed to the * function remains owned by the caller. * @return a reference to the newly created AVHWFramesContext on success or NULL * on failure. */ AVBufferRef *av_hwframe_ctx_alloc(AVBufferRef *device_ctx); /** * Finalize the context before use. This function must be called after the * context is filled with all the required information and before it is attached * to any frames. * * @param ref a reference to the AVHWFramesContext * @return 0 on success, a negative AVERROR code on failure */ int av_hwframe_ctx_init(AVBufferRef *ref); /** * Allocate a new frame attached to the given AVHWFramesContext. * * @param hwframe_ctx a reference to an AVHWFramesContext * @param frame an empty (freshly allocated or unreffed) frame to be filled with * newly allocated buffers. * @param flags currently unused, should be set to zero * @return 0 on success, a negative AVERROR code on failure */ int av_hwframe_get_buffer(AVBufferRef *hwframe_ctx, AVFrame *frame, int flags); /** * Copy data to or from a hw surface. At least one of dst/src must have an * AVHWFramesContext attached. * * If src has an AVHWFramesContext attached, then the format of dst (if set) * must use one of the formats returned by av_hwframe_transfer_get_formats(src, * AV_HWFRAME_TRANSFER_DIRECTION_FROM). * If dst has an AVHWFramesContext attached, then the format of src must use one * of the formats returned by av_hwframe_transfer_get_formats(dst, * AV_HWFRAME_TRANSFER_DIRECTION_TO) * * dst may be "clean" (i.e. with data/buf pointers unset), in which case the * data buffers will be allocated by this function using av_frame_get_buffer(). * If dst->format is set, then this format will be used, otherwise (when * dst->format is AV_PIX_FMT_NONE) the first acceptable format will be chosen. * * The two frames must have matching allocated dimensions (i.e. equal to * AVHWFramesContext.width/height), since not all device types support * transferring a sub-rectangle of the whole surface. The display dimensions * (i.e. AVFrame.width/height) may be smaller than the allocated dimensions, but * also have to be equal for both frames. When the display dimensions are * smaller than the allocated dimensions, the content of the padding in the * destination frame is unspecified. * * @param dst the destination frame. dst is not touched on failure. * @param src the source frame. * @param flags currently unused, should be set to zero * @return 0 on success, a negative AVERROR error code on failure. */ int av_hwframe_transfer_data(AVFrame *dst, const AVFrame *src, int flags); enum AVHWFrameTransferDirection { /** * Transfer the data from the queried hw frame. */ AV_HWFRAME_TRANSFER_DIRECTION_FROM, /** * Transfer the data to the queried hw frame. */ AV_HWFRAME_TRANSFER_DIRECTION_TO, }; /** * Get a list of possible source or target formats usable in * av_hwframe_transfer_data(). * * @param hwframe_ctx the frame context to obtain the information for * @param dir the direction of the transfer * @param formats the pointer to the output format list will be written here. * The list is terminated with AV_PIX_FMT_NONE and must be freed * by the caller when no longer needed using av_free(). * If this function returns successfully, the format list will * have at least one item (not counting the terminator). * On failure, the contents of this pointer are unspecified. * @param flags currently unused, should be set to zero * @return 0 on success, a negative AVERROR code on failure. */ int av_hwframe_transfer_get_formats(AVBufferRef *hwframe_ctx, enum AVHWFrameTransferDirection dir, enum AVPixelFormat **formats, int flags);