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ffmpeg 怎么探测网络流格式/怎么从内存中获取数据

分类: IT文章 • 2022-07-30 21:33:10
ffmpeg 如何探测网络流格式/如何从内存中获取数据

一般ffmpeg都是直接从文件中读取或者从网络流中读取，比如rtp://xx.xx.xx.xx:xxxx。

事实上也支持从内存中获取。

函数avio_alloc_context()实现该功能。

AVIOContext *avio_alloc_context(
                  unsigned char *buffer,
                  int buffer_size,
                  int write_flag,
                  void *opaque,
                  int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),//重写该函数，指定从内存中读取的方法，将buf_size字节大小的数据保存到buf
                  int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),//对应的这是写内存的函数
                  int64_t (*seek)(void *opaque, int64_t offset, int whence));
对于探测网络媒体流个格式，也可以用此种方法，先接收数据，然后探测。

下面贴出代码：

/*
*author tongli
*/
extern "C"{
#include "libavformat/avformat.h"
#include "libavcodec/avcodec.h"
#include "libavutil/avutil.h"
}
#define BUF_SIZE 4096*500

FILE* file;
//实现read_packet函数，从文件中读取模拟的是从内存中获取，同样可以实现为接收网络流
int read_packet(void *opaque, uint8_t *buf, int buf_size)
{
	int n = 0;
	if (!feof(file)){
		n = fread(buf, 1, buf_size, file);
		return n;
	}else
		return -1;
}

int main(int argc, char** argv)
{
	file = fopen("2.mp4", "rb");
	if (file == NULL)
		return -1;
	av_register_all();
	AVIOContext* pb = NULL;
	AVInputFormat* piFmt = NULL;
	AVInputFormat* pFmt = NULL;

	uint8_t* buf = (uint8_t*)av_mallocz(sizeof(uint8_t)* BUF_SIZE);

	pb = avio_alloc_context(buf, BUF_SIZE, 0, NULL, read_packet, NULL, NULL);
	if (av_probe_input_buffer(pb, &piFmt, "", NULL, 0, 0) < 0)//探测从内存中获取到的媒体流的格式
	{
		fprintf(stderr, "probe format failed\n");
		return -1; 
	}
	else{
		fprintf(stdout, "format:%s[%s]\n", piFmt->name, piFmt->long_name);
	}
	return 0;
}
ffmpeg 怎么探测网络流格式/怎么从内存中获取数据
下面实现一个简单的例子，从内存中读取，然后播放。 

<pre name="code" class="cpp">/*
*author tongli
*/
#include <stdio.h>
#include <direct.h>
#include <io.h>
extern "C"{
#include "libavformat/avformat.h"
#include "libavcodec/avcodec.h"
#include "libavutil/avutil.h"
#include "libswscale/swscale.h"
#include "libavformat/avio.h"
#include "sdl/SDL.h"
}
#define BUF_SIZE 4096 * 500
FILE* file;

int read_data(void *opaque, uint8_t *buf, int buf_size)
{
	int n = 0;
	if (!feof(file)){
		n = fread(buf, 1, buf_size, file);
		return n;
	}
	else
		return -1;
}

int main(int argc, char* argv[])
{
	av_register_all();
	//file = fopen("h2.dat", "rb");
	file = fopen("3.mp4", "rb+");
	if (file == NULL)
		return -1;
	AVFormatContext	*pFormatCtx;
	int				i, videoindex;
	AVCodecContext	*pCodecCtx;
	AVCodec			*pCodec;
	AVIOContext* pb = NULL;
	AVInputFormat* piFmt = NULL;

	uint8_t* buf = (uint8_t*)av_mallocz(sizeof(uint8_t)* BUF_SIZE);

	pb = avio_alloc_context(buf, BUF_SIZE, 0, NULL, read_data, NULL, NULL);
	if (av_probe_input_buffer(pb, &piFmt, "", NULL, 0, 0) < 0)
	{
		fprintf(stderr, "probe format failed\n");
		return -1;
	}
	else{
		fprintf(stdout, "format:%s[%s]\n", piFmt->name, piFmt->long_name);
	}
	pFormatCtx = avformat_alloc_context();
	pFormatCtx->pb = pb;

	if (avformat_open_input(&pFormatCtx, "", piFmt, NULL) != 0){//iformat，priv_data赋值，pb, nbstreams,streams为null
		printf("Couldn't open input stream.（无法打开输入流）\n");
		return -1;
	}
	if (avformat_find_stream_info(pFormatCtx, NULL)<0)//nbstreams,streams赋值， pb还是为null
	{
		printf("Couldn't find stream information.（无法获取流信息）\n");
		return -1;
	}
	videoindex = -1;
	for (i = 0; i<pFormatCtx->nb_streams; i++) //一般情况下，一个媒体只有两个流，视频和音频流即streams[0],stream[1]
	if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
	{//找到视频流
		videoindex = i;//在nb_streams视频流的索引
		break;
	}
	if (videoindex == -1)
	{
		printf("Didn't find a video stream.（没有找到视频流）\n");
		return -1;
	}
	pCodecCtx = pFormatCtx->streams[videoindex]->codec;
	pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
	if (pCodec == NULL)
	{
		printf("Codec not found.（没有找到解码器）\n");
		return -1;
	}
	if (avcodec_open2(pCodecCtx, pCodec, NULL)<0)
	{
		printf("Could not open codec.（无法打开解码器）\n");
		return -1;
	}
	AVFrame	*pFrame, *pFrameYUV;
	pFrame = av_frame_alloc();
	pFrameYUV = av_frame_alloc();

	uint8_t *out_buffer;
	out_buffer = new uint8_t[avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height)];
	
	avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
	//------------SDL----------------
	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
		printf("Could not initialize SDL - %s\n", SDL_GetError());
		return -1;
	}
	SDL_Surface *screen;
	screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);
	if (!screen) {
		printf("SDL: could not set video mode - exiting\n");
		return -1;
	}
	SDL_Overlay *bmp;
	bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height, SDL_YV12_OVERLAY, screen);
	SDL_Rect rect;
	//---------------
	int ret, got_picture;
	int y_size = pCodecCtx->width * pCodecCtx->height;

	AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
	av_new_packet(packet, y_size);

	struct SwsContext *img_convert_ctx;
	img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
		AV_PIX_FMT_YUVJ420P/*pCodecCtx->pix_fmt*/, pCodecCtx->width, pCodecCtx->height,
		PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
	//------------------------------
	while (av_read_frame(pFormatCtx, packet) >= 0)
	{
		if (packet->stream_index == videoindex)
		{
			ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
			if (ret < 0)
			{
				printf("Decode Error.（解码错误）\n");
				return -1;
			}
			if (got_picture)
			{
				sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);

				SDL_LockYUVOverlay(bmp);
				bmp->pixels[0] = pFrameYUV->data[0];
				bmp->pixels[2] = pFrameYUV->data[1];
				bmp->pixels[1] = pFrameYUV->data[2];
				bmp->pitches[0] = pFrameYUV->linesize[0];
				bmp->pitches[2] = pFrameYUV->linesize[1];
				bmp->pitches[1] = pFrameYUV->linesize[2];
				SDL_UnlockYUVOverlay(bmp);
				rect.x = 0;
				rect.y = 0;
				rect.w = pCodecCtx->width;
				rect.h = pCodecCtx->height;
				SDL_DisplayYUVOverlay(bmp, &rect);
				//延时40ms
				SDL_Delay(40);
			}
		}
		av_free_packet(packet);
	}
	sws_freeContext(img_convert_ctx);

	delete[] out_buffer;
	av_free(pFrameYUV);
	avcodec_close(pCodecCtx);
	avformat_close_input(&pFormatCtx);

	return 0;
}




															

																					

								

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