参考

大牛对filter的介绍

filter 思想

• filter 架构思想中第一个概念是 Graph，一般翻译为画布，如果 Graph 看做是桌子的话，那 filters 们就是桌子上的“悲剧”。所以先要有 Graph，然后再将 filter 摆在上面， filter是身上有 pin 接口， pin 的作用是统一数据接口，然后还需要一个 link 的动作， link 的作用是将指定的 2 个 filter 通过其 pin 接口连接起来，这样就形成了一个完整的 filter graph或是叫 filter link list。
• 如果只有 filter graph 的存在，它只是一堆参数数据和代码，并不能运行，需要一个动力泵或是动力引擎将整个过程驱动起来，这就像人还缺一颗心脏一样，那人的血液就是filter graph 的数据流。
• 这样 FFmpeg 就把驱动的能力交给了 filter 框架外面来做，通过向 filter graph 的首个 filter 推数据和从 filter graph 的末尾 filter 拉数据从而驱动整个 filter graph 的数据流动。

结构体简介

命令行使用

overlay

命令

ffmpeg -i file_copy.ts -i logo.png -filter_complex "[1:v]scale=100:100[logo];[0:v][logo]overlay=x=main_w-100:y=main_h-100" output.mp4

参数简记

• -filter_complex:滤镜必选参数，后面跟滤镜命令
• [1:v] :输入pin,表示视频的第1路
• scale=100:100 :对[1:v]输入pin的处理，缩放成100:100
• [logo] :输出pin
• ; 每个滤镜分割
• 0:v :两个输入，第一个视频，上一个滤镜的输出
• overlay=x=main_w-100:y=main_h-100 :滤镜动作

效果

结构体认识

/** An instance of a filter */
struct AVFilterContext {const AVClass *av_class;        ///< needed for av_log() and filters common optionsconst AVFilter *filter;         ///< the AVFilter of which this is an instancechar *name;                     ///< name of this filter instanceAVFilterPad   *input_pads;      ///< array of input padsAVFilterLink **inputs;          ///< array of pointers to input linksunsigned    nb_inputs;          ///< number of input padsAVFilterPad   *output_pads;     ///< array of output padsAVFilterLink **outputs;         ///< array of pointers to output linksunsigned    nb_outputs;         ///< number of output padsvoid *priv;                     ///< private data for use by the filterstruct AVFilterGraph *graph;    ///< filtergraph this filter belongs to/*** Type of multithreading being allowed/used. A combination of* AVFILTER_THREAD_* flags.** May be set by the caller before initializing the filter to forbid some* or all kinds of multithreading for this filter. The default is allowing* everything.** When the filter is initialized, this field is combined using bit AND with* AVFilterGraph.thread_type to get the final mask used for determining* allowed threading types. I.e. a threading type needs to be set in both* to be allowed.** After the filter is initialized, libavfilter sets this field to the* threading type that is actually used (0 for no multithreading).*/int thread_type;/*** An opaque struct for libavfilter internal use.*/AVFilterInternal *internal;struct AVFilterCommand *command_queue;char *enable_str;               ///< enable expression stringvoid *enable;                   ///< parsed expression (AVExpr*)double *var_values;             ///< variable values for the enable expressionint is_disabled;                ///< the enabled state from the last expression evaluation/*** For filters which will create hardware frames, sets the device the* filter should create them in.  All other filters will ignore this field:* in particular, a filter which consumes or processes hardware frames will* instead use the hw_frames_ctx field in AVFilterLink to carry the* hardware context information.*/AVBufferRef *hw_device_ctx;/*** Max number of threads allowed in this filter instance.* If <= 0, its value is ignored.* Overrides global number of threads set per filter graph.*/int nb_threads;/*** Ready status of the filter.* A non-0 value means that the filter needs activating;* a higher value suggests a more urgent activation.*/unsigned ready;/*** Sets the number of extra hardware frames which the filter will* allocate on its output links for use in following filters or by* the caller.** Some hardware filters require all frames that they will use for* output to be defined in advance before filtering starts.  For such* filters, any hardware frame pools used for output must therefore be* of fixed size.  The extra frames set here are on top of any number* that the filter needs internally in order to operate normally.** This field must be set before the graph containing this filter is* configured.*/int extra_hw_frames;
};