FFmpeg视频录制

一、Mac 平台 FFmpeg 命令行视频录制

FFmpeg 命令行视频录制的步骤和音频录制步骤类似，首先查看 Mac 平台可用设备：

$ ffmpeg -devices

输出：

Devices:
 D. = Demuxing supported
 .E = Muxing supported
 --
 D  avfoundation    AVFoundation input device
 D  lavfi           Libavfilter virtual input device
  E sdl,sdl2        SDL2 output device

我们选择使用 avfoundation 来录音，接下来查看 avfoundation 支持的设备：

$ ffmpeg -f avfoundation -list_devices true -i ''

输出：

[AVFoundation indev @ 0x7fabb5505300] AVFoundation video devices:
[AVFoundation indev @ 0x7fabb5505300] [0] FaceTime HD Camera
[AVFoundation indev @ 0x7fabb5505300] [1] Capture screen 0
[AVFoundation indev @ 0x7fabb5505300] AVFoundation audio devices:
[AVFoundation indev @ 0x7fabb5505300] [0] Built-in Microphone

我们仅仅是想录制视频，不录制音频，那么选择我的 MacBook pro 自带摄像头 FaceTime HD Camera 就可以，接下来开始录制视频：

$ ffmpeg -f avfoundation -i 0 out.yuv

不出意外终端会输出如下错误：

[avfoundation @ 0x7febb7008200] Selected framerate (29.970030) is not supported by the device.
[avfoundation @ 0x7febb7008200] Supported modes:
[avfoundation @ 0x7febb7008200]   1280x720@[1.000000 30.000000]fps
    Last message repeated 2 times
[avfoundation @ 0x7febb7008200]   640x480@[1.000000 30.000000]fps

意思是设备不支持帧率 29.970030fps，那么重新设置帧率试一下：

$ ffmpeg -f avfoundation -framerate 30 -i 0 out.yuv

输出：

[avfoundation @ 0x7fe4f8008200] Selected pixel format (yuv420p) is not supported by the input device.
[avfoundation @ 0x7fe4f8008200] Supported pixel formats:
[avfoundation @ 0x7fe4f8008200]   uyvy422
[avfoundation @ 0x7fe4f8008200]   yuyv422
[avfoundation @ 0x7fe4f8008200]   nv12
[avfoundation @ 0x7fe4f8008200]   0rgb
[avfoundation @ 0x7fe4f8008200]   bgr0
[avfoundation @ 0x7fe4f8008200] Overriding selected pixel format to use uyvy422 instead.

ffmpeg 的默认像素格式是 yuv420p，但是我们的设备不支持像素格式 yuv420p，支持的格式仅包括 uyvy422、yuyv422、nv12、0rgb 和 bgr0，并且 ffmpeg 自动选择了设备支持的像素格式 uyvy422；

Input #0, avfoundation, from '0':
  Duration: N/A, start: 4916.385400, bitrate: N/A
    Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 320x240, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> rawvideo (native))
Press [q] to stop, [?] for help
Output #0, rawvideo, to 'out_001.yuv':
  Metadata:
    encoder         : Lavf58.45.100
    Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 320x240, q=2-31, 36864 kb/s, 30 fps, 30 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.91.100 rawvideo

此时 ffmpeg 成功的开始采集摄像头的数据了，想要结束的话按下 ctrl + c 就可以。采集的视频像素格式是 uyvy422，分辨率是 320x240，帧率是 30fps。最后播放采集的视频数据：

$ ffplay -pixel_format uyvy422 -video_size 320x240 -framerate 30 out.yuv

PS：查看 avfoundation 支持的参数：

$ ffmpeg -h demuxer=avfoundation

输出：

Demuxer avfoundation [AVFoundation input device]:
AVFoundation indev AVOptions:
  -list_devices      <boolean>    .D........ list available devices (default false)
  -video_device_index <int>        .D........ select video device by index for devices with same name (starts at 0) (from -1 to INT_MAX) (default -1)
  -audio_device_index <int>        .D........ select audio device by index for devices with same name (starts at 0) (from -1 to INT_MAX) (default -1)
  -pixel_format      <pix_fmt>    .D........ set pixel format (default yuv420p)
  -framerate         <video_rate> .D........ set frame rate (default "ntsc")
  -video_size        <image_size> .D........ set video size
  -capture_cursor    <boolean>    .D........ capture the screen cursor (default false)
  -capture_mouse_clicks <boolean>    .D........ capture the screen mouse clicks (default false)
  -capture_raw_data  <boolean>    .D........ capture the raw data from device connection (default false)
  -drop_late_frames  <boolean>    .D........ drop frames that are available later than expected (default true)

二、FFmpeg 编程录制视频

编程录制视频的过程和编程录制音频的过程也很相似，导入需要用到的头文件：

extern "C" {
    #include <libavdevice/avdevice.h>
    #include <libavformat/avformat.h>
    #include <libavcodec/avcodec.h>
    #include <libavutil/avutil.h>
    #include <libavutil/imgutils.h>
}

定义需要的宏定义：

#define FILE_NAME "/Users/mac/Downloads/pic/out.yuv"
#define FMT_NAME "avfoundation"
#define DEVICE_NAME "0"

首先注册所有设备，在整个程序的运行过程中，只需要执行1次注册设备的代码：

avdevice_register_all();

获取输入格式对象：

AVInputFormat *fmt = av_find_input_format(FMT_NAME);
if (!fmt) {
    qDebug() << "not found input format:" << FMT_NAME;
    return;
}

打开输入设备：

// 格式上下文
AVFormatContext *ctx = nullptr;

// 传递给输入设备的参数
AVDictionary *options = nullptr;
av_dict_set(&options, "video_size", "640x480", 0);
av_dict_set(&options, "pixel_format", "yuyv422", 0);
av_dict_set(&options, "framerate", "30", 0);

// 打开输入设备
int ret = avformat_open_input(&ctx, DEVICE_NAME, fmt, &options);
if (ret < 0) {
    char errbuf[1024];
    av_strerror(ret, errbuf, sizeof (errbuf));
    qDebug() << "open input error:" << errbuf;
    return;
}

此处有一个细节，前面使用 FFmpeg 命令行录制的时候，没有设置帧率（-framerate）会报错，我们调用 avformat_open_input 函数的时候也需要设置相应的参数：

AVDictionary *options = nullptr;
av_dict_set(&options, "video_size", "640x480", 0); // 视频像素
av_dict_set(&options, "pixel_format", "yuyv422", 0); // 采样格式
av_dict_set(&options, "framerate", "30", 0); // 帧率

打开文件：

QFile file(FILE_NAME);
if (!file.open(QFile::WriteOnly)) {
    qDebug() << "open file failure:" << FILE_NAME;
    // 关闭输入设备
    avformat_close_input(&ctx);
    return;
}

采集数据：

// 计算每一帧的大小
AVCodecParameters *params = ctx->streams[0]->codecpar;
int imageSize = av_image_get_buffer_size((AVPixelFormat)params->format, params->width, params->height, 1);

// 数据包
AVPacket *pkt = av_packet_alloc();
while (!isInterruptionRequested()) {
    // 不断采集数据
    ret = av_read_frame(ctx, pkt);
    if (ret == 0) {
        // 读取成功，将数据写入文件
        // 这里要使用imageSize，而不是pkt->size。pkt->size有可能比imageSize大（比如在Mac平台），使用pkt->size会导致写入一些多余数据到YUV文件中，进而导致YUV内容无法正常播放
        file.write((const char *)pkt->data, imageSize);
        av_packet_unref(pkt);
    } else if (ret == AVERROR(EAGAIN)) {
        continue;
    } else {
        // 其他错误
        char errbuf[1024];
        av_strerror(ret, errbuf, sizeof (errbuf));
        qDebug() << "read frame error:" << errbuf;
        break;
    }
}

最后释放资源、关闭文件、关闭设备：

// 释放资源
av_packet_free(&pkt);

// 关闭文件
file.close();

// 关闭设备
avformat_close_input(&ctx);