效果如下，这是提取出的音频的播放效果：
主要代码如下
void adts_header(char *szAdtsHeader, int dataLen){
int audio_object_type = 2; // 2是aac LC
int sampling_frequency_index = 4;// 采样频率 44100是0x4
int channel_config = 2;// stero是双声道，左声道+右声道
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;
}
void extra_audio(void){
int err_code;
char errors[1024];
char *src_filename = "/home/chendongpu/demo.mp4";
char *dst_filename = "/home/chendongpu/demo.aac";
FILE *dst_fd = NULL;
int audio_stream_index = -1;
int len;
AVFormatContext *ofmt_ctx = NULL;
AVOutputFormat *output_fmt = NULL;
AVStream *out_stream = NULL;
AVFormatContext *fmt_ctx = NULL;
AVFrame *frame = NULL;
AVPacket pkt;
av_log_set_level(AV_LOG_DEBUG);
// if(argc < 3){
// av_log(NULL, AV_LOG_DEBUG, "the count of parameters should be more than three!\n");
// return -1;
// }
// src_filename = argv[1];
// dst_filename = argv[2];
if(src_filename == NULL || dst_filename == NULL){
av_log(NULL, AV_LOG_DEBUG, "src or dts file is null, plz check them!\n");
return -1;
}
/*register all formats and codec*/
//av_register_all();
/*
ofmt_ctx = avformat_alloc_context();
output_fmt = av_guess_format(NULL, dst_filename, NULL);
if(!output_fmt){
av_log(NULL, AV_LOG_DEBUG, "Cloud not guess file format \n");
exit(1);
}
ofmt_ctx->oformat = output_fmt;
out_stream = avformat_new_stream(ofmt_ctx, NULL);
if(!out_stream){
av_log(NULL, AV_LOG_DEBUG, "Failed to create out stream!\n");
exit(1);
}
if((err_code = avio_open(&ofmt_ctx->pb, dst_filename, AVIO_FLAG_WRITE)) < 0) {
av_strerror(err_code, errors, 1024);
av_log(NULL, AV_LOG_DEBUG, "Could not open file %s, %d(%s)\n",
dst_filename,
err_code,
errors);
exit(1);
}
*/
dst_fd = fopen(dst_filename, "wb+");
if (!dst_fd) {
av_log(NULL, AV_LOG_DEBUG, "Could not open destination file %s\n", dst_filename);
return -1;
}
/*open input media file, and allocate format context*/
if((err_code = avformat_open_input(&fmt_ctx, src_filename, NULL, NULL)) < 0){
av_strerror(err_code, errors, 1024);
av_log(NULL, AV_LOG_DEBUG, "Could not open source file: %s, %d(%s)\n",
src_filename,
err_code,
errors);
return -1;
}
/*retrieve audio stream*/
if((err_code = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
av_strerror(err_code, errors, 1024);
av_log(NULL, AV_LOG_DEBUG, "failed to find stream information: %s, %d(%s)\n",
src_filename,
err_code,
errors);
return -1;
}
/*dump input information*/
av_dump_format(fmt_ctx, 0, src_filename, 0);
/*dump output information*/
//av_dump_format(ofmt_ctx, 0, dst_filename, 1);
frame = av_frame_alloc();
if(!frame){
av_log(NULL, AV_LOG_DEBUG, "Could not allocate frame\n");
return AVERROR(ENOMEM);
}
/*initialize packet*/
av_init_packet(&pkt);
pkt.data = NULL;
pkt.size = 0;
/*find best audio stream*/
audio_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
if(audio_stream_index < 0){
av_log(NULL, AV_LOG_DEBUG, "Could not find %s stream in input file %s\n",
av_get_media_type_string(AVMEDIA_TYPE_AUDIO),
src_filename);
return AVERROR(EINVAL);
}
/*
if (avformat_write_header(ofmt_ctx, NULL) < 0) {
av_log(NULL, AV_LOG_DEBUG, "Error occurred when opening output file");
exit(1);
}
*/
/*read frames from media file*/
while(av_read_frame(fmt_ctx, &pkt) >=0 ){
if(pkt.stream_index == audio_stream_index){
/*
pkt.stream_index = 0;
av_write_frame(ofmt_ctx, &pkt);
av_free_packet(&pkt);
*/
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_DEBUG, "warning, length of writed data isn't equal pkt.size(%d, %d)\n",
len,
pkt.size);
}
}
av_packet_unref(&pkt);
}
//av_write_trailer(ofmt_ctx);
/*close input media file*/
avformat_close_input(&fmt_ctx);
if(dst_fd) {
fclose(dst_fd);
}
return;
}
完整代码
