【FFmpeg之AVOption】编码选项设置

一、AVOption简介

AVOption是FFmpeg的选项设置工具。AVOption的核心概念就是“根据字符串操作结构体的属性值”。与AVOption最相关的选项设置函数就是av_opt_set()了。

二、av_opt_set()函数详解

int av_opt_set         (void *obj, const char *name, const char *val, int search_flags);
int av_opt_set_int     (void *obj, const char *name, int64_t     val, int search_flags);
int av_opt_set_double  (void *obj, const char *name, double      val, int search_flags);
int av_opt_set_q       (void *obj, const char *name, AVRational  val, int search_flags);
int av_opt_set_bin     (void *obj, const char *name, const uint8_t *val, int size, int search_flags);
int av_opt_set_image_size(void *obj, const char *name, int w, int h, int search_flags);
int av_opt_set_pixel_fmt (void *obj, const char *name, enum AVPixelFormat fmt, int search_flags);
int av_opt_set_sample_fmt(void *obj, const char *name, enum AVSampleFormat fmt, int search_flags);
int av_opt_set_video_rate(void *obj, const char *name, AVRational val, int search_flags);
int av_opt_set_channel_layout(void *obj, const char *name, int64_t ch_layout, int search_flags);

参数1：obj是一个结构体，第一个元素是指向AVClass结构体的指针
参数2：要设置参数的字段名
参数3：设置的值
参数4：子结构体的标志（可忽略）

两种方式作用相同

#if TEST_OPT
	av_opt_set(pCodecCtx,"b","400000",0);		//bitrate
	//Another method
	//av_opt_set_int(pCodecCtx,"b",400000,0);	//bitrate
 
	av_opt_set(pCodecCtx,"time_base","1/25",0);	//time_base
	av_opt_set(pCodecCtx,"bf","5",0);			//max b frame
	av_opt_set(pCodecCtx,"g","25",0);			//gop
	av_opt_set(pCodecCtx,"qmin","10",0);		//qmin/qmax
	av_opt_set(pCodecCtx,"qmax","51",0);
#else
	pCodecCtx->time_base.num = 1;  
	pCodecCtx->time_base.den = 25;  
	pCodecCtx->max_b_frames=5;
	pCodecCtx->bit_rate = 400000;  
	pCodecCtx->gop_size=25;
	pCodecCtx->qmin = 10;
	pCodecCtx->qmax = 51;
#endif