FFmpeg入门教程10.22：音视频解混合（demuxer）为PCM和YUV420P

系列索引：FFmpeg入门系列索引

上一篇：FFmpeg入门教程10.21：音视频解混合（demuxer）为MP3和H264

可以看出本文要在上一篇的基础上将MP3解码为pcm，将h264解码为yuv。

操作流程为：

flowchart TB

A(开始) --> B[打开文件]
B --> C[查找流信息]
C --> D[查找解码器]
C --> E[创建输出文件]
D --> F[打开解码器]
E --> G[打开输出文件]
G --> J[查找输出流]
J --> K[创建流]
K --> L[写入文件]
F --> H{读取帧}
H --Yes--> M[解码]
M --> L
L --读取下一帧--> H
H --No--> I(结束)

对应的函数调用流程为

flowchart TB

A(Start) --> B[avformat_open_input]
B --> C[avformat_find_stream_info]
C --> D[avcodec_find_decoder]
D --> E[avcodec_aloc_context3]
E --> F[avcodec_open2]
F --> G[swr_alloc_set_opts]
F --> H[sws_getContext]
G & H --> I{av_read_frame}
I --Yes--> K[avcodec_send_packet]
K --> L[avcodec_receive_frame]
L --> M[swr_convert]
L --> N[sws_scale]
M & N --> O[frwrite]
O --Next Frame--> I
I --No--> J(End)

首先是每次都有的，打开与查找

1
2
3
4
5
6
7
8
9
10
11
12
13
//2.打开输入文件
if (avformat_open_input(&pFormatCtx, inputFile, NULL, NULL) != 0)
{
    printf("can't open input file\n");
    return -1;
}

//3.获取音视频信息
if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
{
    printf("can't find stream info\n");
    return -1;
}

界面音频部分

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
104
105
106
107
108
109
110
111
112
113
114
int avcodec_save_audio_file(AVFormatContext *pFormatCtx, int streamIndex, char *fileName)
{
    AVCodec *pCodec;
    AVCodecContext *pCodecCtx;
    AVCodecParameters *codecpar = pFormatCtx->streams[streamIndex]->codecpar;

    //4.获取解码器（一）:音频
    //根据索引拿到对应的流
    pCodec = avcodec_find_decoder(codecpar->codec_id);
    if (!pCodec)
    {
        printf("can't decoder audio\n");
        return -1;
    }
    //申请一个解码上下文
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (!pCodecCtx)
    {
        printf("can't allocate a audio decoding context\n");
        return -1;
    }

    //用流解码信息初始化编码参数
    avcodec_parameters_to_context(pCodecCtx, codecpar);

    //没有此句会出现：Could not update timestamps for skipped samples
    pCodecCtx->pkt_timebase = pFormatCtx->streams[streamIndex]->time_base;

    //5.打开解码器
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
    {
        printf("can't open codec\n");
        return -1;
    }

//	printf("--------------- File Information ----------------\n");
//	av_dump_format(pFormatCtx, 0, fileName, 0);
//	printf("-------------------------------------------------\n");

    //编码数据
    AVPacket *packet = (AVPacket*) av_malloc(sizeof(AVPacket));
    //解压缩数据
    AVFrame *frame = av_frame_alloc();

    //frame->16bit 44100 PCM统一音频采样格式与采样率
    SwrContext *swrCtx = swr_alloc();
    //重采样设置选项-----------------------------------------------------------start
    //输入的采样格式
    AVSampleFormat inSampleFmt = pCodecCtx->sample_fmt;
    //输出的采样格式
    AVSampleFormat outSampleFmt = AV_SAMPLE_FMT_S16;
    //输入的采样率
    int inSampleRate = pCodecCtx->sample_rate;
    //输出的采样率
    int outSampleRate = 44100;
    //输入的声道布局
    uint64_t inChannelLayout = pCodecCtx->channel_layout;
    //输出的声道布局：CHANNEL_IN_MONO为单声道，CHANNEL_IN_STEREO为双声道
    uint64_t outChannelLayout = AV_CH_LAYOUT_MONO;

    printf("inSampleFmt = %d, inSampleRate = %d, inChannelLayout = %d， name = %s\n", inSampleFmt, inSampleRate,
            (int) inChannelLayout, pCodec->name);

    swr_alloc_set_opts(swrCtx, outChannelLayout, outSampleFmt, outSampleRate,
            inChannelLayout, inSampleFmt, inSampleRate, 0, NULL);
    swr_init(swrCtx);
    //重采样设置选项-----------------------------------------------------------end

    //获取输出的声道个数
    int outChannelNb = av_get_channel_layout_nb_channels(outChannelLayout);
    printf("outChannelNb = %d\n", outChannelNb);

    //存储PCM数据
    uint8_t *outBuffer = (uint8_t*) av_malloc(2 * 44100);

    FILE *fp = fopen(fileName, "wb");

    //回到流的初始位置
    av_seek_frame(pFormatCtx, streamIndex, 0, AVSEEK_FLAG_BACKWARD);

    //6.一帧一帧读取压缩的音频数据AVPacket
    while (av_read_frame(pFormatCtx, packet) >= 0)
    {
        if (packet->stream_index == streamIndex)
        {
            //解码AVPacket --> AVFrame
            int ret = avcodec_send_packet(pCodecCtx, packet);
            if (ret < 0)
            {
                printf("Decode error\n");
                break;
            }

            if (avcodec_receive_frame(pCodecCtx, frame) >= 0)
            {
                swr_convert(swrCtx, &outBuffer, 2 * 44100, (const uint8_t**) frame->data, frame->nb_samples);
                //获取sample的size
                int outBufferSize = av_samples_get_buffer_size(NULL, outChannelNb, frame->nb_samples, outSampleFmt, 1);
                //写入文件
                fwrite(outBuffer, 1, outBufferSize, fp);
            }
        }

        av_packet_unref(packet);
    }

    fclose(fp);
    av_frame_free(&frame);
    av_free(outBuffer);
    swr_free(&swrCtx);
    avcodec_close(pCodecCtx);

    return 0;
}

解码视频部分

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
int avcodec_save_video_file(AVFormatContext *pFormatCtx, int streamIndex, char *fileName)
{
    AVCodec *pCodec;
    AVCodecContext *pCodecCtx;
    AVCodecParameters *codecpar = pFormatCtx->streams[streamIndex]->codecpar;

    //4.获取解码器（一）:视频
    //根据索引拿到对应的流
    pCodec = avcodec_find_decoder(codecpar->codec_id);
    if (!pCodec)
    {
        printf("can't decoder audio\n");
        return -1;
    }
    //申请一个解码上下文
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (!pCodecCtx)
    {
        printf("can't allocate a audio decoding context\n");
        return -1;
    }

    //用流解码信息初始化编码参数
    avcodec_parameters_to_context(pCodecCtx, codecpar);

    //没有此句会出现：Could not update timestamps for skipped samples
//	pCodecCtx->pkt_timebase = pFormatCtx->streams[streamIndex]->time_base;

    //5.打开解码器
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
    {
        printf("can't open codec\n");
        return -1;
    }

//	printf("--------------- File Information ----------------\n");
//	av_dump_format(pFormatCtx, 0, fileName, 0);
//	printf("-------------------------------------------------\n");

    //编码数据
    AVPacket *pPacket = (AVPacket*) av_malloc(sizeof(AVPacket));
    //解压缩数据
    AVFrame *pFrame = av_frame_alloc();
    AVFrame *pFrameYUV = av_frame_alloc();

    unsigned char *outBuffer = (unsigned char*) av_malloc(
            av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1));
    av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize, outBuffer,
            AV_PIX_FMT_YUV420P, pCodecCtx->width,
            pCodecCtx->height, 1);

    SwsContext *pImgConvertCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
            pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);

    printf("width = %d, height = %d, name = %s\n", pCodecCtx->width, pCodecCtx->height, pCodec->name);

    FILE *fp = fopen(fileName, "wb+");

    //回到流的初始位置
    av_seek_frame(pFormatCtx, streamIndex, 0, AVSEEK_FLAG_BACKWARD);

    //6.一帧一帧读取压缩的视频数据AVPacket
    while (av_read_frame(pFormatCtx, pPacket) >= 0)
    {
        if (pPacket->stream_index == streamIndex)
        {
            //解码AVPacket --> AVFrame
            int ret = avcodec_send_packet(pCodecCtx, pPacket);
            if (ret < 0)
            {
                printf("Decode error\n");
                break;
            }

            if (avcodec_receive_frame(pCodecCtx, pFrame) >= 0)
            {
                sws_scale(pImgConvertCtx, pFrame->data, pFrame->linesize, 0,
                        pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);

                int y_size = pCodecCtx->width * pCodecCtx->height;
                fwrite(pFrameYUV->data[0], 1, y_size, fp);    //Y
                fwrite(pFrameYUV->data[1], 1, y_size / 4, fp);  //U
                fwrite(pFrameYUV->data[2], 1, y_size / 4, fp);  //V
            }
        }

        av_packet_unref(pPacket);
    }

    fclose(fp);
    av_frame_free(&pFrame);
    av_frame_free(&pFrameYUV);
    av_free(outBuffer);
    avcodec_close(pCodecCtx);

    return 0;
}

最终得到*.pcm，*.yuv文件

我们测试一下结果。

result

播放测试

pcm音频播放

result

yuv视频播放

result

完整代码在ffmpeg_beginner中的10.22.video_demuxer_mp42yuvpcm。

下一篇：FFmpeg入门教程10.23：音视频mp3和h264混合（muxer）编码为mp4

FFmpeg
#FFmpeg #解码 #YUV420P #PCM #解混合
FFmpeg入门教程10.22：音视频解混合（demuxer）为PCM和YUV420P
https://blog.jackeylea.com/ffmpeg/ffmpeg-demuxer-video-to-pcm-and-yuv420p/
作者
JackeyLea
发布于
2021年5月23日
许可协议