音视频开发_FFmpeg 提取AAC ADTS
FFmpeg提取AAC ADTS
ADTS流结构
代码流程
- 为了使ADTS播放正常，需要手动加入ADTS头部
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const int sampling_frequencies[] = {
96000, // 0x0
88200, // 0x1
64000, // 0x2
48000, // 0x3
44100, // 0x4
32000, // 0x5
24000, // 0x6
22050, // 0x7
16000, // 0x8
12000, // 0x9
11025, // 0xa
8000 // 0xb
// 0xc d e f是保留的
};
int adts_header(char * const p_adts_header, const int data_length,
const int profile, const int samplerate,
const int channels)
{
int sampling_frequency_index = 3; // 默认使用48000hz
int adtsLen = data_length + 7;
int frequencies_size = sizeof(sampling_frequencies) / sizeof(sampling_frequencies[0]);
int i = 0;
for(i = 0; i < frequencies_size; i++)
{
if(sampling_frequencies[i] == samplerate)
{
sampling_frequency_index = i;
break;
}
}
if(i >= frequencies_size)
{
printf("unsupport samplerate:%d\n", samplerate);
return -1;
}
p_adts_header[0] = 0xff; //syncword:0xfff 高8bits
p_adts_header[1] = 0xf0; //syncword:0xfff 低4bits
p_adts_header[1] |= (0 << 3); //MPEG Version:0 for MPEG-4,1 for MPEG-2 1bit
p_adts_header[1] |= (0 << 1); //Layer:0 2bits
p_adts_header[1] |= 1; //protection absent:1 1bit
p_adts_header[2] = (profile)<<6; //profile:profile 2bits
p_adts_header[2] |= (sampling_frequency_index & 0x0f)<<2; //sampling frequency index:sampling_frequency_index 4bits
p_adts_header[2] |= (0 << 1); //private bit:0 1bit
p_adts_header[2] |= (channels & 0x04)>>2; //channel configuration:channels 高1bit
p_adts_header[3] = (channels & 0x03)<<6; //channel configuration:channels 低2bits
p_adts_header[3] |= (0 << 5); //original：0 1bit
p_adts_header[3] |= (0 << 4); //home：0 1bit
p_adts_header[3] |= (0 << 3); //copyright id bit：0 1bit
p_adts_header[3] |= (0 << 2); //copyright id start：0 1bit
p_adts_header[3] |= ((adtsLen & 0x1800) >> 11); //frame length：value 高2bits
p_adts_header[4] = (uint8_t)((adtsLen & 0x7f8) >> 3); //frame length:value 中间8bits
p_adts_header[5] = (uint8_t)((adtsLen & 0x7) << 5); //frame length:value 低3bits
p_adts_header[5] |= 0x1f; //buffer fullness:0x7ff 高5bits
p_adts_header[6] = 0xfc; //11111100 //buffer fullness:0x7ff 低6bits
// number_of_raw_data_blocks_in_frame：
// 表示ADTS帧中有number_of_raw_data_blocks_in_frame + 1个AAC原始帧。
return 0;
} - 每次先将头部写入到aac文件中，再写入帧体数据
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21// 读取媒体文件，并把aac数据帧写入到本地文件
while(av_read_frame(ifmt_ctx, &pkt) >=0 )
{
if(pkt.stream_index == audio_index)
{
char adts_header_buf[7] = {0};
adts_header(adts_header_buf, pkt.size,
ifmt_ctx->streams[audio_index]->codecpar->profile,
ifmt_ctx->streams[audio_index]->codecpar->sample_rate,
ifmt_ctx->streams[audio_index]->codecpar->channels);
fwrite(adts_header_buf, 1, 7, aac_fd); // 写adts header , ts流不适用，ts流分离出来的packet带了adts header
len = fwrite( pkt.data, 1, pkt.size, aac_fd); // 写adts data
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);
}
对MP4文件运行结果
