前言

在FFmpeg开源工程中添加一个新的AVFilter包括6个基本步骤。下面以maskfun 为例进行说明。

1 在libavfilter目录下添加实现文件

如果是video filter，则文件名以vf_开头；如果是audio filter，则文件名以af_开头，本例中是 vf_maskfun.c。具体实现内容这里不展开。

2 在libavfilter/allfilters.c中添加外部声明

allfilters.c中包含所有AVFilter全局变量的外部声明。在合适的位置按字母排序添加新的AVFilter。

extern AVFilter ff_vf_maskedclamp;
extern AVFilter ff_vf_maskedmerge;
extern AVFilter ff_vf_maskfun;
extern AVFilter ff_vf_mcdeint;

3 在libavfilter/Makefile中添加相关指令

OBJS-$(CONFIG_MASKEDCLAMP_FILTER)            += vf_maskedclamp.o framesync.o
OBJS-$(CONFIG_MASKEDMERGE_FILTER)            += vf_maskedmerge.o framesync.o
OBJS-$(CONFIG_MASKFUN_FILTER)                += vf_maskfun.o
OBJS-$(CONFIG_MCDEINT_FILTER)                += vf_mcdeint.o

4 在libavfilter/version.h中修改版本号

将LIBAVFILTER_VERSION_MINOR加1，LIBAVFILTER_VERSION_MICRO重置为100

#define LIBAVFILTER_VERSION_MAJOR   7
#define LIBAVFILTER_VERSION_MINOR  48
#define LIBAVFILTER_VERSION_MICRO 100

5 在Changelog中增加一条记录

在Changelog的version <next>:区域的最下方增加新filter的记录

version <next>:
- tpad filter
- AV1 decoding support through libdav1d
- dedot filter
- chromashift and rgbashift filters
- freezedetect filter
- truehd_core bitstream filter
- dhav demuxer
- PCM-DVD encoder
- GIF parser
- vividas demuxer
- hymt decoder
- anlmdn filter
- maskfun filter

6 在doc/filters.texi中补充文档说明

@section maskfun
Create mask from input video.

For example it is useful to create motion masks after @code{tblend} filter.

This filter accepts the following options:

@table @option
@item low
Set low threshold. Any pixel component lower or exact than this value will be set to 0.

@item high
Set high threshold. Any pixel component higher than this value will be set to max value
allowed for current pixel format.

@item planes
Set planes to filter, by default all available planes are filtered.

@item fill
Fill all frame pixels with this value.

@item sum
Set max average pixel value for frame. If sum of all pixel components is higher that this
average, output frame will be completely filled with value set by @var{fill} option.
Typically useful for scene changes when used in combination with @code{tblend} filter.
@end table

在FFmpeg中添加一个AVFilter

前言