ffmpeg提取aac数据

方法1：通过命令提取

 ffmpeg -i input.mp4 -vn -acodec aac ../output.aac

方法2：通过代码提取

流程图

 

 

main.c　　

#include "libavutil/log.h"
#include "libavformat/avformat.h"
#include "libavutil/avutil.h"


static int get_audio_obj_type(int aac_type) {
    //AAC HE V2 = AAC LC + SBR + PS
    //AAV HE = AAC LC + SBR
    //所以无论是 AAC_HEv2 还是 AAC_HE 都是 AAC_LC
    if (aac_type == 0 || aac_type == 2 || aac_type == 3) {
        return aac_type + 1;
    } else {
        return 2;
    }
}

static int get_sample_rate_index(int freq, int aac_type) {

    int i;
    int freq_arr[13] = {
            96000, 88200, 64000, 48000, 44100, 32000,
            24000, 22050, 16000, 12000, 11025, 8000, 7350
    };

    //如果是 AAC HEv2 或 AAC HE, 则频率减半
    if (aac_type == 28 || aac_type == 4) {
        freq /= 2;
    }

    for (i = 0; i < 13; i++) {
        if (freq == freq_arr[i]) {
            return i;
        }
    }
    return 4;//默认是44100
}

static int get_channel_config(int channels, int aac_type) {
    //如果是 AAC HEv2 通道数减半
    if (aac_type == 28) {
        return (channels / 2);
    }
    return channels;
}

void getADTSHeader(uint8_t *adtsHeader, int packetSize, int profile, int sampleRate, int channels) {
    int audio_object_type = get_audio_obj_type(profile);
    int sampling_frequency_index = get_sample_rate_index(sampleRate, profile);
    int channel_config = get_channel_config(channels, profile);


    int adtsLen = packetSize + 7;

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

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

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

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

int main(int argc, char **argv) {
    av_log_set_level(AV_LOG_DEBUG);
    if (argc < 3) {
        av_log(NULL, AV_LOG_ERROR, "Usage: %s inputFile outputFile\n", argv[0]);
        return -1;
    }
    const char *inputFile = argv[1];
    const char *outputFile = argv[2];
    AVFormatContext *fCtx = NULL;

    int ret = avformat_open_input(&fCtx, inputFile, NULL, NULL);
    if (ret != 0) {
        av_log(NULL, AV_LOG_ERROR, "Open input file %s failed: %s\n", inputFile, av_err2str(ret));
        return -1;
    }
    ret = avformat_find_stream_info(fCtx, NULL);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Find input file stream info failed: %s\n", av_err2str(ret));
        avformat_close_input(&fCtx);
        return -1;
    }
    int audioIndex = av_find_best_stream(fCtx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
    if (audioIndex < 0) {
        av_log(NULL, AV_LOG_ERROR, "Find best stream failed: %d\n", audioIndex);
        avformat_close_input(&fCtx);
        return -1;
    }
    av_log(NULL, AV_LOG_INFO, "audioIndex=%d\n", audioIndex);
    FILE *dst = fopen(outputFile, "wb");
    if (dst == NULL) {
        av_log(NULL, AV_LOG_ERROR, "Open output file: %s failed\n", outputFile);
        avformat_close_input(&fCtx);
        return -1;
    }
    AVPacket *packet = av_packet_alloc();
    packet->data = NULL;
    packet->size = 0;
    while (av_read_frame(fCtx, packet) == 0) {
        if (packet->stream_index == audioIndex) {
            uint8_t header[7] = {0};
            getADTSHeader(header,
                          packet->size, fCtx->streams[audioIndex]->codecpar->profile,
                          fCtx->streams[audioIndex]->codecpar->sample_rate,
                          fCtx->streams[audioIndex]->codecpar->channels);
            size_t size = fwrite(header, sizeof(uint8_t), sizeof(header), dst);
            if (size != sizeof(header)) {
                av_log(NULL, AV_LOG_ERROR, "Write ADTS header size: %zu, expected size: %lu\n", size, sizeof(header));
                fclose(dst);
                avformat_close_input(&fCtx);
                return -1;
            }
            size = fwrite(packet->data, sizeof(uint8_t), packet->size, dst);
            if (size != packet->size) {
                av_log(NULL, AV_LOG_ERROR, "Write size: %zu, packet size: %d\n", size, packet->size);
                fclose(dst);
                avformat_close_input(&fCtx);
                return -1;
            }
        }
        av_packet_unref(packet);
    }

    if (fCtx != NULL) {
        avformat_close_input(&fCtx);
    }
    fclose(dst);

    return 0;
}

　　

　

Makefile

TARGET=main
SRC=main.c
CC=gcc
CFLAGS=-I /usr/local/ffmpeg/include
LDFLAGS=-L /usr/local/ffmpeg/lib
LDFLAGS+= -lavutil -lavformat -lavcodec
all:$(TARGET)
$(TARGET):$(SRC)
	$(CC) $(SRC) $(CFLAGS) $(LDFLAGS) -o $(TARGET)
clean:
	rm -rf $(TARGET)