ffmpeg抽取音频数据

最新推荐文章于 2024-09-04 00:01:42 发布

zJianFlys

最新推荐文章于 2024-09-04 00:01:42 发布

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分类专栏： FFmpeg 文章标签： c++

本文链接：https://blog.youkuaiyun.com/ZHOU452840622/article/details/120518055

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#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avformat.h>

void adts_header(char *szAdtsHeader, int dataLen){

    int audio_object_type = 2;
    int sampling_frequency_index = 7;
    int channel_config = 2;

    int adtsLen = dataLen + 7;

    szAdtsHeader[0] = 0xff;         //syncword:0xfff                          高8bits
    szAdtsHeader[1] = 0xf0;         //syncword:0xfff                          低4bits
    szAdtsHeader[1] |= (0 << 3);    //MPEG Version:0 for MPEG-4,1 for MPEG-2  1bit
    szAdtsHeader[1] |= (0 << 1);    //Layer:0                                 2bits 
    szAdtsHeader[1] |= 1;           //protection absent:1                     1bit

    szAdtsHeader[2] = (audio_object_type - 1)<<6;            //profile:audio_object_type - 1                      2bits
    szAdtsHeader[2] |= (sampling_frequency_index & 0x0f)<<2; //sampling frequency index:sampling_frequency_index  4bits 
    szAdtsHeader[2] |= (0 << 1);                             //private bit:0                                      1bit
    szAdtsHeader[2] |= (channel_config & 0x04)>>2;           //channel configuration:channel_config               高1bit

    szAdtsHeader[3] = (channel_config & 0x03)<<6;     //channel configuration:channel_config      低2bits
    szAdtsHeader[3] |= (0 << 5);                      //original：0                               1bit
    szAdtsHeader[3] |= (0 << 4);                      //home：0                                   1bit
    szAdtsHeader[3] |= (0 << 3);                      //copyright id bit：0                       1bit  
    szAdtsHeader[3] |= (0 << 2);                      //copyright id start：0                     1bit
    szAdtsHeader[3] |= ((adtsLen & 0x1800) >> 11);           //frame length：value   高2bits

    szAdtsHeader[4] = (uint8_t)((adtsLen & 0x7f8) >> 3);     //frame length:value    中间8bits
    szAdtsHeader[5] = (uint8_t)((adtsLen & 0x7) << 5);       //frame length:value    低3bits
    szAdtsHeader[5] |= 0x1f;                                 //buffer fullness:0x7ff 高5bits
    szAdtsHeader[6] = 0xfc;
}

int main(int argc,char *argv[])
{
	int ret;
	int len;
	int audio_index;
	char* src = NULL;
	char* dst = NULL;
	AVPacket pkt;
	AVFormatContext *fmt_ctx = NULL;
	av_log_set_level(AV_LOG_INFO);
	
	//1.read two params from console
	if(argc < 3){
		av_log(NULL,AV_LOG_ERROR,"the count of params should be more than three!\n");
	}
	
	src = argv[1];
	dst = argv[2];
	if(!src || !dst){
		av_log(NULL,AV_LOG_ERROR,"src or dst is null!\n");
		return -1;
	}
	
	ret = avformat_open_input(&fmt_ctx, src, NULL, NULL);
	if(ret<0){
		av_log(NULL,AV_LOG_ERROR,"Can't open file:%s\n",av_err2str(ret));
		return -1;
	}
	
	FILE* dst_fd = fopen(dst,"wb");
	if(!dst_fd){
		av_log(NULL,AV_LOG_ERROR,"Can't open out file!\n");
		avformat_close_input(&fmt_ctx);
		return -1;
	}
	
	av_dump_format(fmt_ctx, 0, src, 0);

	//2.get stream 
	ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
	if(ret < 0){
		av_log(NULL,AV_LOG_ERROR,"Can't find the best stream!\n");
		avformat_close_input(&fmt_ctx);
		fclose(dst_fd);
		return -1;
	}
	
	audio_index = ret;
	/*initialize packet*/
	//av_init_packet(&pkt);
	while(av_read_frame(fmt_ctx, &pkt) >= 0){
		if(pkt.stream_index == audio_index){
			char adts_header_buf[7];
			adts_header(adts_header_buf, pkt.size);
			fwrite(adts_header_buf, 1, 7, dst_fd);
			//3. write audio data to aac file.
			len = fwrite(pkt.data, 1, pkt.size, dst_fd);
			if(len != pkt.size){
				av_log(NULL,AV_LOG_WARNING,"warning, length of data is not equal size of pkt!\n");
			}
		}
		av_packet_unref(&pkt);
	}
	
	avformat_close_input(&fmt_ctx);
	if(dst_fd){
		fclose(dst_fd);
	}
	return 0;
}

编译文件：

gcc -g -o extra_audio extra_audio.c `pkg-config --cflags --libs libavformat libavutil`

输入媒体文件：

./eatra_audio paly.mp4 audio.aac

学习来源：https://coding.imooc.com/lesson/279.html#mid=18316