上一篇已經寫了如何配置好開發環境，這次就先小試牛刀，來個視訊的編碼。搞視訊處理的朋友肯定比較熟悉YUV視訊序列，很多測試庫提供的視訊資料都是YUV視訊序列，我們這裡就用用YUV視訊序列來做視訊。關於YUV視訊序列，我就不多講了，可以看書學習，通常的視訊序列都是YUV420格式的。

步驟也就那幾步，新增視訊流，開啟編碼器，開闢相應的記憶體空間，然後就可以開啟YUV序列逐幀寫入資料了，so easy！記得最後要做好檔案的關閉和記憶體的釋放，因為FFmpeg是c風格的（不知道新版本是否是c++風格的），這些工作都需要自己做好啊。過多的說明是沒用的，直接上程式碼：

這裡我補充一下，大多數的視訊格式好像只支援YUV格式的視訊幀AVFrame，我試圖直接把RGB的視訊序列直接編碼到視訊這條路好像走不通，都需要把RGB的視訊幀再轉成YUV視訊幀才行，

#include <stdio.h>
#include <string.h>

extern "C"
{
#include <libavcodec\avcodec.h>
#include <libavformat\avformat.h>
#include <libswscale\swscale.h>
};

void main(int argc, char ** argv)
{
	AVFormatContext* oc;
	AVOutputFormat* fmt;
	AVStream* video_st;
	double video_pts;
	uint8_t* video_outbuf;
	uint8_t* picture_buf;
	AVFrame* picture;
// 	AVFrame* pictureRGB;
	int size;
	int ret;
	int video_outbuf_size;

	FILE *fin = fopen("akiyo_qcif.yuv", "rb"); //視訊原始檔 

	const char* filename = "test.mpg";
// 	const char* filename;
// 	filename = argv[1];

	av_register_all();

// 	avcodec_init(); // 初始化codec庫
// 	avcodec_register_all(); // 註冊編碼器

	fmt = guess_format(NULL, filename, NULL);
	oc = av_alloc_format_context();
	oc->oformat = fmt;
	snprintf(oc->filename, sizeof(oc->filename), "%s", filename);

	video_st = NULL;
	if (fmt->video_codec != CODEC_ID_NONE)
	{
		AVCodecContext* c;
		video_st = av_new_stream(oc, 0);
		c = video_st->codec;
		c->codec_id = fmt->video_codec;
		c->codec_type = CODEC_TYPE_VIDEO;
		c->bit_rate = 400000;
		c->width = 176;
		c->height = 144;
		c->time_base.num = 1;
		c->time_base.den = 25; 
		c->gop_size = 12;
		c->pix_fmt = PIX_FMT_YUV420P;
		if (c->codec_id == CODEC_ID_MPEG2VIDEO)
		{
			c->max_b_frames = 2;
		}
		if (c->codec_id == CODEC_ID_MPEG1VIDEO)
		{
			c->mb_decision = 2;
		}
		if (!strcmp(oc->oformat->name, "mp4") || !strcmp(oc->oformat->name, "mov") || !strcmp(oc->oformat->name, "3gp"))
		{
			c->flags |= CODEC_FLAG_GLOBAL_HEADER;
		}
	}

	if (av_set_parameters(oc, NULL)<0)
	{
		return;
	}
	
	dump_format(oc, 0, filename, 1);
	if (video_st)
	{
		AVCodecContext* c;
		AVCodec* codec;
		c = video_st->codec;
		codec = avcodec_find_encoder(c->codec_id);
		if (!codec)
		{
			return;
		}
		if (avcodec_open(c, codec) < 0)
		{
			return;
		}
		if (!(oc->oformat->flags & AVFMT_RAWPICTURE))
		{
			video_outbuf_size = 200000;
			video_outbuf = (uint8_t*)av_malloc(video_outbuf_size);
		}
		picture = avcodec_alloc_frame();
		size = avpicture_get_size(c->pix_fmt, c->width, c->height);
		picture_buf = (uint8_t*)av_malloc(size);
		if (!picture_buf)
		{
			av_free(picture);
		}
		avpicture_fill((AVPicture*)picture, picture_buf, c->pix_fmt, c->width, c->height);
	}

	if (!(fmt->flags & AVFMT_NOFILE))
	{
		if (url_fopen(&oc->pb, filename, URL_WRONLY) < 0)
		{
			return;
		}
	}
	av_write_header(oc);

	for (int i=0; i<300; i++)
	{
		if (video_st)
		{
			video_pts = (double)(video_st->pts.val * video_st->time_base.num / video_st->time_base.den);
		}
		else
		{
			video_pts = 0.0;
		}
		if (!video_st/* || video_pts >= 5.0*/)
		{
			break;
		}
		AVCodecContext* c;
		c = video_st->codec;
		size = c->width * c->height;

		if (fread(picture_buf, 1, size*3/2, fin) < 0)
		{
			break;
		}
		
		picture->data[0] = picture_buf;  // 亮度
		picture->data[1] = picture_buf+ size;  // 色度 
		picture->data[2] = picture_buf+ size*5/4; // 色度 

		// 如果是rgb序列，可能需要如下程式碼
// 		SwsContext* img_convert_ctx;
// 		img_convert_ctx = sws_getContext(c->width, c->height, PIX_FMT_RGB24, c->width, c->height, c->pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
// 		sws_scale(img_convert_ctx, pictureRGB->data, pictureRGB->linesize, 0, c->height, picture->data, picture->linesize);

		if (oc->oformat->flags & AVFMT_RAWPICTURE)
		{
			AVPacket pkt;
			av_init_packet(&pkt);
			pkt.flags |= PKT_FLAG_KEY;
			pkt.stream_index = video_st->index;
			pkt.data = (uint8_t*)picture;
			pkt.size = sizeof(AVPicture);
			ret = av_write_frame(oc, &pkt);
		}
		else
		{
			int out_size = avcodec_encode_video(c, video_outbuf, video_outbuf_size, picture);
			if (out_size > 0)
			{
				AVPacket pkt;
				av_init_packet(&pkt);
				pkt.pts = av_rescale_q(c->coded_frame->pts, c->time_base, video_st->time_base);
				if (c->coded_frame->key_frame)
				{
					pkt.flags |= PKT_FLAG_KEY;
				}
				pkt.stream_index = video_st->index;
				pkt.data = video_outbuf;
				pkt.size = out_size;
				ret = av_write_frame(oc, &pkt);
			}
		}
	}

	if (video_st)
	{
		avcodec_close(video_st->codec);
// 		av_free(picture->data[0]);
		av_free(picture);
		av_free(video_outbuf);
// 		av_free(picture_buf);
	}
	av_write_trailer(oc);
	for (int i=0; i<oc->nb_streams; i++)
	{
		av_freep(&oc->streams[i]->codec);
		av_freep(&oc->streams[i]);
	}
	if (!(fmt->flags & AVFMT_NOFILE))
	{
		url_fclose(oc->pb);
	}
	av_free(oc);
}