本章主要介绍AVBSF
从名字我们可以知道这是个码流过滤器,我们最常用的是一个叫做h264_mp4toannexb_bsf的东东
这个过滤器的作用是把h264以MP4格式的NALU转换为annexb(0x000001)
const AVBitStreamFilter ff_h264_mp4toannexb_bsf = {
.name = "h264_mp4toannexb",
.priv_data_size = sizeof(H264BSFContext),
.init = h264_mp4toannexb_init,
.filter = h264_mp4toannexb_filter,
.flush = h264_mp4toannexb_flush,
.codec_ids = codec_ids,
};
/**
* @addtogroup lavc_core
* @{
*/
/**
* The bitstream filter state.
*
* This struct must be allocated with av_bsf_alloc() and freed with
* av_bsf_free().
*
* The fields in the struct will only be changed (by the caller or by the
* filter) as described in their documentation, and are to be considered
* immutable otherwise.
*/
typedef struct AVBSFContext {
/**
* A class for logging and AVOptions
*/
const AVClass *av_class;
/**
* The bitstream filter this context is an instance of.
*/
const struct AVBitStreamFilter *filter;
/**
* Opaque filter-specific private data. If filter->priv_class is non-NULL,
* this is an AVOptions-enabled struct.
*/
void *priv_data;
/**
* Parameters of the input stream. This field is allocated in
* av_bsf_alloc(), it needs to be filled by the caller before
* av_bsf_init().
*/
AVCodecParameters *par_in;
/**
* Parameters of the output stream. This field is allocated in
* av_bsf_alloc(), it is set by the filter in av_bsf_init().
*/
AVCodecParameters *par_out;
/**
* The timebase used for the timestamps of the input packets. Set by the
* caller before av_bsf_init().
*/
AVRational time_base_in;
/**
* The timebase used for the timestamps of the output packets. Set by the
* filter in av_bsf_init().
*/
AVRational time_base_out;
} AVBSFContext;
上面是bsf的上下文,下面的是它的插件回调函数
typedef struct AVBitStreamFilter {
const char *name;
/**
* A list of codec ids supported by the filter, terminated by
* AV_CODEC_ID_NONE.
* May be NULL, in that case the bitstream filter works with any codec id.
*/
const enum AVCodecID *codec_ids;
/**
* A class for the private data, used to declare bitstream filter private
* AVOptions. This field is NULL for bitstream filters that do not declare
* any options.
*
* If this field is non-NULL, the first member of the filter private data
* must be a pointer to AVClass, which will be set by libavcodec generic
* code to this class.
*/
const AVClass *priv_class;
/*****************************************************************
* No fields below this line are part of the public API. They
* may not be used outside of libavcodec and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
int priv_data_size;
int (*init)(AVBSFContext *ctx);
int (*filter)(AVBSFContext *ctx, AVPacket *pkt);
void (*close)(AVBSFContext *ctx);
void (*flush)(AVBSFContext *ctx);
} AVBitStreamFilter;
看多了就会发现非常相似,基本就一个套路,一个上下文结构体,一个回调插件结构体,上下文中一个私有的指针,大小为priv_data_size,所以如果想要实现插件,简单的实现这几个回调函数就可以了。
核心对外函数
/**
* @return a bitstream filter with the specified name or NULL if no such
* bitstream filter exists.
*/
const AVBitStreamFilter *av_bsf_get_by_name(const char *name);
/**
* Iterate over all registered bitstream filters.
*
* @param opaque a pointer where libavcodec will store the iteration state. Must
* point to NULL to start the iteration.
*
* @return the next registered bitstream filter or NULL when the iteration is
* finished
*/
const AVBitStreamFilter *av_bsf_iterate(void **opaque);
/**
* Allocate a context for a given bitstream filter. The caller must fill in the
* context parameters as described in the documentation and then call
* av_bsf_init() before sending any data to the filter.
*
* @param filter the filter for which to allocate an instance.
* @param ctx a pointer into which the pointer to the newly-allocated context
* will be written. It must be freed with av_bsf_free() after the
* filtering is done.
*
* @return 0 on success, a negative AVERROR code on failure
*/
int av_bsf_alloc(const AVBitStreamFilter *filter, AVBSFContext **ctx);
/**
* Prepare the filter for use, after all the parameters and options have been
* set.
*/
int av_bsf_init(AVBSFContext *ctx);
/**
* Submit a packet for filtering.
*
* After sending each packet, the filter must be completely drained by calling
* av_bsf_receive_packet() repeatedly until it returns AVERROR(EAGAIN) or
* AVERROR_EOF.
*
* @param pkt the packet to filter. The bitstream filter will take ownership of
* the packet and reset the contents of pkt. pkt is not touched if an error occurs.
* If pkt is empty (i.e. NULL, or pkt->data is NULL and pkt->side_data_elems zero),
* it signals the end of the stream (i.e. no more non-empty packets will be sent;
* sending more empty packets does nothing) and will cause the filter to output
* any packets it may have buffered internally.
*
* @return 0 on success. AVERROR(EAGAIN) if packets need to be retrieved from the
* filter (using av_bsf_receive_packet()) before new input can be consumed. Another
* negative AVERROR value if an error occurs.
*/
int av_bsf_send_packet(AVBSFContext *ctx, AVPacket *pkt);
/**
* Retrieve a filtered packet.
*
* @param[out] pkt this struct will be filled with the contents of the filtered
* packet. It is owned by the caller and must be freed using
* av_packet_unref() when it is no longer needed.
* This parameter should be "clean" (i.e. freshly allocated
* with av_packet_alloc() or unreffed with av_packet_unref())
* when this function is called. If this function returns
* successfully, the contents of pkt will be completely
* overwritten by the returned data. On failure, pkt is not
* touched.
*
* @return 0 on success. AVERROR(EAGAIN) if more packets need to be sent to the
* filter (using av_bsf_send_packet()) to get more output. AVERROR_EOF if there
* will be no further output from the filter. Another negative AVERROR value if
* an error occurs.
*
* @note one input packet may result in several output packets, so after sending
* a packet with av_bsf_send_packet(), this function needs to be called
* repeatedly until it stops returning 0. It is also possible for a filter to
* output fewer packets than were sent to it, so this function may return
* AVERROR(EAGAIN) immediately after a successful av_bsf_send_packet() call.
*/
int av_bsf_receive_packet(AVBSFContext *ctx, AVPacket *pkt);
/**
* Reset the internal bitstream filter state. Should be called e.g. when seeking.
*/
void av_bsf_flush(AVBSFContext *ctx);
/**
* Free a bitstream filter context and everything associated with it; write NULL
* into the supplied pointer.
*/
void av_bsf_free(AVBSFContext **ctx);
其实这些函数内部也很简单,主要就是对回调函数的封装。
extern const AVBitStreamFilter ff_aac_adtstoasc_bsf;
extern const AVBitStreamFilter ff_av1_frame_merge_bsf;
extern const AVBitStreamFilter ff_av1_frame_split_bsf;
extern const AVBitStreamFilter ff_av1_metadata_bsf;
extern const AVBitStreamFilter ff_chomp_bsf;
extern const AVBitStreamFilter ff_dump_extradata_bsf;
extern const AVBitStreamFilter ff_dca_core_bsf;
extern const AVBitStreamFilter ff_eac3_core_bsf;
extern const AVBitStreamFilter ff_extract_extradata_bsf;
extern const AVBitStreamFilter ff_filter_units_bsf;
extern const AVBitStreamFilter ff_h264_metadata_bsf;
extern const AVBitStreamFilter ff_h264_mp4toannexb_bsf;
extern const AVBitStreamFilter ff_h264_redundant_pps_bsf;
extern const AVBitStreamFilter ff_hapqa_extract_bsf;
extern const AVBitStreamFilter ff_hevc_metadata_bsf;
extern const AVBitStreamFilter ff_hevc_mp4toannexb_bsf;
extern const AVBitStreamFilter ff_imx_dump_header_bsf;
extern const AVBitStreamFilter ff_mjpeg2jpeg_bsf;
extern const AVBitStreamFilter ff_mjpega_dump_header_bsf;
extern const AVBitStreamFilter ff_mp3_header_decompress_bsf;
extern const AVBitStreamFilter ff_mpeg2_metadata_bsf;
extern const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf;
extern const AVBitStreamFilter ff_mov2textsub_bsf;
extern const AVBitStreamFilter ff_noise_bsf;
extern const AVBitStreamFilter ff_null_bsf;
extern const AVBitStreamFilter ff_opus_metadata_bsf;
extern const AVBitStreamFilter ff_pcm_rechunk_bsf;
extern const AVBitStreamFilter ff_prores_metadata_bsf;
extern const AVBitStreamFilter ff_remove_extradata_bsf;
extern const AVBitStreamFilter ff_setts_bsf;
extern const AVBitStreamFilter ff_text2movsub_bsf;
extern const AVBitStreamFilter ff_trace_headers_bsf;
extern const AVBitStreamFilter ff_truehd_core_bsf;
extern const AVBitStreamFilter ff_vp9_metadata_bsf;
extern const AVBitStreamFilter ff_vp9_raw_reorder_bsf;
extern const AVBitStreamFilter ff_vp9_superframe_bsf;
extern const AVBitStreamFilter ff_vp9_superframe_split_bsf;