使用ffmpeg库实现，抽取视频中的音频信息，并进行保存
//// Created by andrew on /11/1.//#include <iostream>extern "C" {#include <libavutil/log.h>#include <libavformat/avformat.h>}// aac每帧开头都要填写对应的格式信息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8bitsszAdtsHeader[1] = 0xf0; //syncword:0xfff低4bitsszAdtsHeader[1] |= (0 << 3); //MPEG Version:0 for MPEG-4,1 for MPEG-2 1bitszAdtsHeader[1] |= (0 << 1); //Layer:0 2bitsszAdtsHeader[1] |= 1; //protection absent:1 1bitszAdtsHeader[2] = (audio_object_type - 1)<<6; //profile:audio_object_type - 1 2bitsszAdtsHeader[2] |= (sampling_frequency_index & 0x0f)<<2; //sampling frequency index:sampling_frequency_index 4bitsszAdtsHeader[2] |= (0 << 1); //private bit:0 1bitszAdtsHeader[2] |= (channel_config & 0x04)>>2; //channel configuration:channel_config高1bitszAdtsHeader[3] = (channel_config & 0x03)<<6;//channel configuration:channel_config低2bitsszAdtsHeader[3] |= (0 << 5); //original：0 1bitszAdtsHeader[3] |= (0 << 4); //home：01bitszAdtsHeader[3] |= (0 << 3); //copyright id bit：0 1bitszAdtsHeader[3] |= (0 << 2); //copyright id start：0 1bitszAdtsHeader[3] |= ((adtsLen & 0x1800) >> 11); //frame length：value 高2bitsszAdtsHeader[4] = (uint8_t)((adtsLen & 0x7f8) >> 3);//frame length:value 中间8bitsszAdtsHeader[5] = (uint8_t)((adtsLen & 0x7) << 5); //frame length:value 低3bitsszAdtsHeader[5] |= 0x1f; //buffer fullness:0x7ff 高5bitsszAdtsHeader[6] = 0xfc;}/** 从多媒体文件中抽取媒体信息* */int main(int argc, char *argv[]) {AVFormatContext *fmt_ctx = NULL;av_log_set_level(AV_LOG_INFO);/*所有进行操作前，先执行以下，否则需要自己制定类型*/av_register_all();// 1. 读取多媒体文件char *pSrc = NULL;char *pDst = NULL;pSrc = (char *)"/work/test/test.mp4";pDst = "test.aac";/*Open an input stream and read the header*/int ret = avformat_open_input(&fmt_ctx, "/work/test/test.mp4", NULL, NULL);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "can't open file.\n");return -1;}// write audio data to AAC fileFILE *dst_fd = fopen(pDst, "wb");if (dst_fd == NULL) {av_log(NULL, AV_LOG_ERROR, "open dst_fd failed.\n");avformat_close_input(&fmt_ctx);return -1;}/** Print detailed information about the input or output format* */av_dump_format(fmt_ctx, 0, "/work/test/test.mp4", 0);// 2. get streamret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "ret = %d\n", ret);avformat_close_input(&fmt_ctx);fclose(dst_fd);return -1;}int audio_index = -1;audio_index = ret;AVPacket pkt;/*Initialize optional fields of a packet with default values.*/av_init_packet(&pkt);int len = -1;/*保存原始数据，播放时需要添加AAC的音频格式说明的头*/while (av_read_frame(fmt_ctx, &pkt) >= 0) {if (pkt.stream_index == audio_index) {/*每帧开头都要写*/char adts_header_buf[7];adts_header(adts_header_buf, pkt.size);fwrite(adts_header_buf, 1, 7, dst_fd);len = fwrite(pkt.data, 1, pkt.size, dst_fd);if (len != pkt.size) {av_log(NULL, AV_LOG_ERROR, "waning, length is not equl size of pkt.\n");return -1;}}/*Wipe the packet.*/av_packet_unref(&pkt);}/**//*Close an opened input AVFormatContext*/avformat_close_input(&fmt_ctx);if (dst_fd != NULL)fclose(dst_fd);return 0;}
需要注意的是，源码中的test.mp4一定要写对路径
执行结果
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/work/test/test.mp4':Metadata:major_brand: isomminor_version : 512compatible_brands: isomiso2avc1mp41track : 0artist: 段奥娟album : comment : 163 key(Don't modify):ZWxeTBkln0EQUjdDVUZQXrJzMh33POt0FgWTvjgge2X8BzXmyZaXb9C8+H2VGrdLG7XRTMrkXzzfV9VNH7sp0KlFimbjkVbsWksXY5YrzqFNXeJX1gvrBWCV+m3aYddkvy0HxucdcxCoCrYsrnzxL97sgxi0M2VHh6PREC3j6Uz4hfWkIMGhul9aszAuzEvbUUIQXSZRHgpkVW3g3oTEwqY5CexOWMIgIZAjlFIMxtitle : 元気满分encoder : Lavf57.71.100Duration: 00:03:46.80, bitrate: N/AStream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 854x480, 687 kb/s, SAR 1:1 DAR 427:240, 25 fps, 25 tbr, 12800 tbn (default)Metadata:handler_name : VideoHandlerStream #0:1(zho): Audio: aac (mp4a / 0x6134706D), 44100 Hz, 2 channels, 125 kb/s (default)Metadata:handler_name : SoundHandler
