原文地址: http://blog.csdn.net/wh8_2011/article/details/73506154
本文实现: 读取PC摄像头视频数据并以RTMP协议发送为直播流. 示例包含 1. FFmpeg的libavdevice的使用 2. 视频编码, 解码, 推流的基本流程
要使用libavdevice的相关函数, 首先需要注册相关组件 avdevice_register_all()
列出电脑中可用的DShow设备
AVFormatContext *pFmtCtx = avformat_alloc_context();
AVDeviceInfoList *device_info = NULL;
AVDictionary* options = NULL;
av_dict_set(&options, "list_devices", "true", 0);
AVInputFormat *iformat = av_find_input_format("dshow");
printf("Device Info=============\n");
avformat_open_input(&pFmtCtx, "video=dummy", iformat, &options);
printf("========================\n");
也可以直接使用FFmpeg的工具 ffmpeg -list_devices true -f dshow -i dummy
PS: avdevice有一个avdevice_list_devices函数可以枚举系统的采集设备, 包括设备名和设备描述, 可以让用户选择要使用的设备, 但是不支持DShow设备.
像打开普通文件一样将上面的具体设备名作为输入打开, 并进行相应的初始化设置
av_register_all();
//Register Device
avdevice_register_all();
avformat_network_init();
//Show Dshow Device
show_dshow_device();
printf("\nChoose capture device: ");
if (gets(capture_name) == 0)
{
printf("Error in gets()\n");
return -1;
}
sprintf(device_name, "video=%s", capture_name);
ifmt=av_find_input_format("dshow");
//Set own video device's name
if (avformat_open_input(&ifmt_ctx, device_name, ifmt, NULL) != 0){
printf("Couldn't open input stream.（无法打开输入流）\n");
return -1;
}
//input initialize
if (avformat_find_stream_info(ifmt_ctx, NULL)<0)
{
printf("Couldn't find stream information.（无法获取流信息）\n");
return -1;
}
videoindex = -1;
for (i = 0; i<ifmt_ctx->nb_streams; i++)
if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
videoindex = i;
break;
}
if (videoindex == -1)
{
printf("Couldn't find a video stream.（没有找到视频流）\n");
return -1;
}
if (avcodec_open2(ifmt_ctx->streams[videoindex]->codec, avcodec_find_decoder(ifmt_ctx->streams[videoindex]->codec->codec_id), NULL)<0)
{
printf("Could not open codec.（无法打开解码器）\n");
return -1;
}
输入设备初始化后, 需要对输出做相应的初始化. FFmpeg将网络协议和文件同等看待, 同时因为使用RTMP协议进行传输, 因此制定输出为flv格式, 编码器使用H.264
//output initialize
avformat_alloc_output_context2(&ofmt_ctx, NULL, "flv", out_path);
//output encoder initialize
pCodec = avcodec_find_encoder(AV_CODEC_ID_H264);
if (!pCodec){
printf("Can not find encoder! (没有找到合适的编码器！)\n");
return -1;
}
pCodecCtx=avcodec_alloc_context3(pCodec);
pCodecCtx->pix_fmt = PIX_FMT_YUV420P;
pCodecCtx->width = ifmt_ctx->streams[videoindex]->codec->width;
pCodecCtx->height = ifmt_ctx->streams[videoindex]->codec->height;
pCodecCtx->time_base.num = 1;
pCodecCtx->time_base.den = 25;
pCodecCtx->bit_rate = 400000;
pCodecCtx->gop_size = 250;
/* Some formats,for example,flv, want stream headers to be separate. */
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
pCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;
//H264 codec param
//pCodecCtx->me_range = 16;
//pCodecCtx->max_qdiff = 4;
//pCodecCtx->qcompress = 0.6;
pCodecCtx->qmin = 10;
pCodecCtx->qmax = 51;
//Optional Param
pCodecCtx->max_b_frames = 3;
// Set H264 preset and tune
AVDictionary *param = 0;
av_dict_set(¶m, "preset", "fast", 0);
av_dict_set(¶m, "tune", "zerolatency", 0);
if (avcodec_open2(pCodecCtx, pCodec,¶m) < 0){
printf("Failed to open encoder! (编码器打开失败！)\n");
return -1;
}
//Add a new stream to output,should be called by the user before avformat_write_header() for muxing
video_st = avformat_new_stream(ofmt_ctx, pCodec);
if (video_st == NULL){
return -1;
}
video_st->time_base.num = 1;
video_st->time_base.den = 25;
video_st->codec = pCodecCtx;
//Open output URL,set before avformat_write_header() for muxing
if (avio_open(&ofmt_ctx->pb,out_path, AVIO_FLAG_READ_WRITE) < 0){
printf("Failed to open output file! (输出文件打开失败！)\n");
return -1;
}
//Show some Information
av_dump_format(ofmt_ctx, 0, out_path, 1);
//Write File Header
avformat_write_header(ofmt_ctx,NULL);
完成输入和输出的初始化后, 就可以正式开始解码和编码并推流的流程了. 需要注意的是, 摄像头数据往往是RGB格式的, 需要将其转换为YUV420P格式, 才能推流, 因此要先做如下的准备工作
//prepare before decode and encode
dec_pkt = (AVPacket *)av_malloc(sizeof(AVPacket));
//enc_pkt = (AVPacket *)av_malloc(sizeof(AVPacket));
//camera data has a pix fmt of RGB,convert it to YUV420
img_convert_ctx = sws_getContext(ifmt_ctx->streams[videoindex]->codec->width, ifmt_ctx->streams[videoindex]->codec->height,
ifmt_ctx->streams[videoindex]->codec->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
pFrameYUV = avcodec_alloc_frame();
uint8_t *out_buffer = (uint8_t *)av_malloc(avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
现在, 就可以正式开始解码, 编码 和推流了
//start decode and encode
int64_t start_time=av_gettime();
while (av_read_frame(ifmt_ctx, dec_pkt) >= 0){
if (exit_thread)
break;
av_log(NULL, AV_LOG_DEBUG, "Going to reencode the frame\n");
pframe = av_frame_alloc();
if (!pframe) {
ret = AVERROR(ENOMEM);
return -1;
}
//av_packet_rescale_ts(dec_pkt, ifmt_ctx->streams[dec_pkt->stream_index]->time_base,
// ifmt_ctx->streams[dec_pkt->stream_index]->codec->time_base);
ret = avcodec_decode_video2(ifmt_ctx->streams[dec_pkt->stream_index]->codec, pframe,
&dec_got_frame, dec_pkt);
if (ret < 0) {
av_frame_free(&pframe);
av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
break;
}
if (dec_got_frame){
sws_scale(img_convert_ctx, (const uint8_t* const*)pframe->data, pframe->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
enc_pkt.data = NULL;
enc_pkt.size = 0;
av_init_packet(&enc_pkt);
ret = avcodec_encode_video2(pCodecCtx, &enc_pkt, pFrameYUV, &enc_got_frame);
av_frame_free(&pframe);
if (enc_got_frame == 1){
//printf("Succeed to encode frame: %5d\tsize:%5d\n", framecnt, enc_pkt.size);
framecnt++;
enc_pkt.stream_index = video_st->index;
//Write PTS
AVRational time_base = ofmt_ctx->streams[videoindex]->time_base;//{ 1, 1000 };
AVRational r_framerate1 = ifmt_ctx->streams[videoindex]->r_frame_rate;// { 50, 2 };
AVRational time_base_q = { 1, AV_TIME_BASE };
//Duration between 2 frames (us)
int64_t calc_duration = (double)(AV_TIME_BASE)*(1 / av_q2d(r_framerate1)); //内部时间戳
//Parameters
//enc_pkt.pts = (double)(framecnt*calc_duration)*(double)(av_q2d(time_base_q)) / (double)(av_q2d(time_base));
enc_pkt.pts = av_rescale_q(framecnt*calc_duration, time_base_q, time_base);
enc_pkt.dts = enc_pkt.pts;
enc_pkt.duration = av_rescale_q(calc_duration, time_base_q, time_base); //(double)(calc_duration)*(double)(av_q2d(time_base_q)) / (double)(av_q2d(time_base));
enc_pkt.pos = -1;
//Delay
int64_t pts_time = av_rescale_q(enc_pkt.dts, time_base, time_base_q);
int64_t now_time = av_gettime() - start_time;
if (pts_time > now_time)
av_usleep(pts_time - now_time);
ret = av_interleaved_write_frame(ofmt_ctx, &enc_pkt);
av_free_packet(&enc_pkt);
}
}
else {
av_frame_free(&pframe);
}
av_free_packet(dec_pkt);
}
解码比较简单, 编码部分需要自己计算PTS, DTS, 比较复杂 这里通过帧率计算PTS和DTS, 首先通过帧率计算两帧之间的时间间隔, 但是要换算