【FFMPEG】从视频文件中抽取aac数据写成文件

这篇博客主要记录的是

• 如何打开视频文件
• 如何写文件
• 如何从AVFormatContext中抽取aac数据
• 如何写出AAC数据
• 如何生成AAC Header

	extern "C" {
	#include 
	#include 
	#include 
	#include 
	}
	
	#include 
	#include 
	
	int buildAdtsHeader(char *const header, const int dataLength, const int profile, const int samplerate, const int channels) {
	    //采样率编号
	    std::map<int, int> samplerateMap;
	    samplerateMap.insert(std::make_pair(96000, 0x0));
	    samplerateMap.insert(std::make_pair(88200, 0x1));
	    samplerateMap.insert(std::make_pair(64000, 0x2));
	    samplerateMap.insert(std::make_pair(48000, 0x3));
	    samplerateMap.insert(std::make_pair(44100, 0x4));
	    samplerateMap.insert(std::make_pair(32000, 0x5));
	    samplerateMap.insert(std::make_pair(24000, 0x6));
	    samplerateMap.insert(std::make_pair(22050, 0x7));
	    samplerateMap.insert(std::make_pair(16000, 0x8));
	    samplerateMap.insert(std::make_pair(12000, 0x9));
	    samplerateMap.insert(std::make_pair(11025, 0xa));
	    samplerateMap.insert(std::make_pair(8000, 0xb));
	    int samplerateCode = samplerateMap.find(samplerate)->second;
	
	    //生成Header
	    int frameLength = dataLength + 7;
	
	    header[0] = 0xff;  //syncword:0xff
	    header[1] = 0xf0;
	    header[1] |= (0 << 3);  //MPEG Version: 0 MPEG-4, 1 MPEG-2, 1bit
	    header[1] |= (0 << 1);  //Layer: 0, 2bit
	    header[1] |= 1;  //protection absent: 1, 1bit
	
	    header[2] = (profile) << 6;  //profile: aac profile, 2bit
	    header[2] |= (samplerateCode & 0x0f) << 2;  //samplerate, 4bit
	    header[2] |= (0 << 1);  //private bit: 0, 1bit
	    header[2] |= (channels & 0x04) >> 2;  //channels, 1bit
	
	    header[3] = (channels & 0x03) << 6;  //channels, 2bit
	    header[3] |= (0 << 5);  //original: 0, 1bit
	    header[3] |= (0 << 4);  //home: 0, 1bit
	    header[3] |= (0 << 3);  //copyright id bit: 0, 1bit
	    header[3] |= (0 << 2);  //copyright id start: 0, 1bit
	    header[3] |= ((frameLength & 0x1800) >> 11);  //frame length part1, 2bit
	
	    header[4] = (uint8_t)((frameLength & 0x7f8) >> 3);  //frame length part2, 8bit
	    header[5] = (uint8_t)((frameLength & 0x7) << 5);  //frame length part3, 3bit
	    header[5] |= 0x1f;  //buffer fullness part1, 5bit
	    header[6] = 0xfc;  //‭buffer fullness part2, 6bit
	
	    return 0;
	}
	
	int main() {
	    char *inputFile = "G:/src.mp4";
	    char *outputFile = "G:/dst.aac";
	    FILE *aacFile = fopen(outputFile, "wb+");
	
	    //打开视频文件
	    AVFormatContext *avFormatContext = NULL;
	    avformat_open_input(&avFormatContext, inputFile, NULL, NULL);
	
	    //探测流信息
	    avformat_find_stream_info(avFormatContext, NULL);
	
	    //获取音频流
	    int audioStreamIndex = av_find_best_stream(avFormatContext, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
	    AVStream *audioStream = avFormatContext->streams[audioStreamIndex];
	
	    //创建并初始化AVPacket
	    AVPacket *packet = av_packet_alloc();
	    av_init_packet(packet);
	
	    //读取文件，把aac数据写入文件
	    while (av_read_frame(avFormatContext, packet) >= 0) {
	        if (packet->stream_index != audioStreamIndex)
	            continue;
	        //创建AVPacket对应的头部
	        char header[7] = {};
	        buildAdtsHeader(header, packet->size, audioStream->codecpar->profile, audioStream->codecpar->sample_rate, audioStream->codecpar->channels);
	        //写入AVPacket的Header和Body
	        //如果是TS流的数据话，AVPacket本身已经携带Header了，不需要再写入
	        fwrite(header, 1, 7, aacFile);
	        fwrite(packet->data, 1, packet->size, aacFile);
	        //解除一个引用计数
	        av_packet_unref(packet);
	    }
	
	    //关闭和释放资源
	    av_free_packet(packet);
	    if (avFormatContext)
	        avformat_close_input(&avFormatContext);
	    if (aacFile)
	        fclose(aacFile);
	
	    return 0;
	}


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103