例如，我们想要把一个经过降噪处理后的输出文件与输入原文件进行比较，如果不使用带连接标号的滤镜图，我们需要至少两条命令：
ffmpeg -i input.mpg -vf hqdn3d,pad=2*iw output.mp4
ffmpeg -i output.mp4 -i input.mpg -filter_complex overlay=w compare.mp4
如果使用带有连接标号的滤镜图，则一条命令就可以了：
ffplay -i i.mpg -vf split[a][b];[a]pad=2*iw[A];[b]hqdn3d[B];[A][B]overlay=w
滤镜(广义)通常以滤镜链(filterchain, 以逗号分隔的滤镜序列)和滤镜图(filtergraph, 以分号分隔的滤镜序列)的形式使用。滤镜链由滤镜构成，滤镜图由滤镜链构成，这样可以提供复杂多样的组合方式以应对不同的应用场景。
滤镜(狭义)是滤镜链的简单特例，滤镜链是滤镜图的简单特例。注意这里滤镜(狭义)、滤镜链、滤镜图之间不是继承的关系，而是组合的关系，比如，一个滤镜图可以只包含一个滤镜链，而一个滤镜链也可以只包含一个滤镜，这种特例情况下，一个滤镜图仅由单个滤镜构成。FFmpeg的命令行中，滤镜(广义)的出现形式有滤镜(狭义)、滤镜链、滤镜图三种形式，但滤镜(狭义)和滤镜链可以看作是特殊的滤镜图，因此，为了简便，FFmpeg的命令行中滤镜相关选项，只针对滤镜图(filtergraph)概念，分为如下两类：
针对简单滤镜图的选项：“-vf”等同“-filter:v”，“-af”等同“-filter:a”
针对复杂滤镜图的选项：“-lavfi”等价“-filter_complex”
待补充
struct AVFilter
/** * Filter definition. This defines the pads a filter contains, and all the * callback functions used to interact with the filter. */ typedef struct AVFilter { const char *name; const char *description; const AVFilterPad *inputs; const AVFilterPad *outputs; const AVClass *priv_class; int flags; // private API ...... } AVFilter;struct AVFilterContext
/** An instance of a filter */ struct AVFilterContext { const AVClass *av_class; ///< needed for av_log() and filters common options const AVFilter *filter; ///< the AVFilter of which this is an instance char *name; ///< name of this filter instance AVFilterPad *input_pads; ///< array of input pads AVFilterLink **inputs; ///< array of pointers to input links unsigned nb_inputs; ///< number of input pads AVFilterPad *output_pads; ///< array of output pads AVFilterLink **outputs; ///< array of pointers to output links unsigned nb_outputs; ///< number of output pads void *priv; ///< private data for use by the filter struct AVFilterGraph *graph; ///< filtergraph this filter belongs to ...... };struct AVFilterGraph
typedef struct AVFilterGraph { const AVClass *av_class; AVFilterContext **filters; unsigned nb_filters; ...... } AVFilterGraph;struct AVFilterLink
/** * A link between two filters. This contains pointers to the source and * destination filters between which this link exists, and the indexes of * the pads involved. In addition, this link also contains the parameters * which have been negotiated and agreed upon between the filter, such as * image dimensions, format, etc. * * Applications must not normally access the link structure directly. * Use the buffersrc and buffersink API instead. * In the future, access to the header may be reserved for filters * implementation. */ struct AVFilterLink { AVFilterContext *src; ///< source filter AVFilterPad *srcpad; ///< output pad on the source filter AVFilterContext *dst; ///< dest filter AVFilterPad *dstpad; ///< input pad on the dest filter ...... }struct AVFilterInOut
/** * A linked-list of the inputs/outputs of the filter chain. * * This is mainly useful for avfilter_graph_parse() / avfilter_graph_parse2(), * where it is used to communicate open (unlinked) inputs and outputs from and * to the caller. * This struct specifies, per each not connected pad contained in the graph, the * filter context and the pad index required for establishing a link. */ typedef struct AVFilterInOut { /** unique name for this input/output in the list */ char *name; /** filter context associated to this input/output */ AVFilterContext *filter_ctx; /** index of the filt_ctx pad to use for linking */ int pad_idx; /** next input/input in the list, NULL if this is the last */ struct AVFilterInOut *next; } AVFilterInOut;