利用ffmpeg的api 从电影中截图

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// tutorial01.c
// Code based on a tutorial by Martin Bohme ([email protected])
// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1

// A small sample program that shows how to use libavformat and libavcodec to
// read video from a file.
//
// Use
//
// gcc -o tutorial01 tutorial01.c -lavformat -lavcodec -lz
//
// to build (assuming libavformat and libavcodec are correctly installed
// your system).
//
// Run using
//
// tutorial01 myvideofile.mpg
//
// to write the first five frames from "myvideofile.mpg" to disk in PPM
// format.

#include 
#include 
#include 

#include 
static const char* file = "/home/cmzx3444/a.rmvb";

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame)
{
	FILE *pFile;
	char szFilename[32];
	int y;

	// Open file
	sprintf(szFilename, "/home/cmzx3444/a%d.ppm", iFrame);
	pFile = fopen(szFilename, "wb");
	if (pFile == NULL)
		return;

	// Write header
	fprintf(pFile, "P6\n%d %d\n255\n", width, height);

	// Write pixel data
	for (y = 0; y < height; y++)
		fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width * 3, pFile);

	// Close file
	fclose(pFile);
}

int main(int argc, char *argv[])
{
	AVFormatContext *pFormatCtx;
	int i, videoStream;
	AVCodecContext *pCodecCtx;
	AVCodec *pCodec;
	AVFrame *pFrame;
	AVFrame *pFrameRGB;
	AVPacket packet;
	int frameFinished;
	int numBytes;
	uint8_t *buffer;
	// Register all formats and codecs
	av_register_all();

	// Open video file
	if (av_open_input_file(&pFormatCtx, file, NULL, 0, NULL) != 0)
		return -1; // Couldn't open file
	// Retrieve stream information
	if (av_find_stream_info(pFormatCtx) < 0)
		return -1; // Couldn't find stream information

	// Dump information about file onto standard error
	dump_format(pFormatCtx, 0, file, 0);

	// Find the first video stream
	videoStream = -1;
	for (i = 0; i < pFormatCtx->nb_streams; i++)
		if (pFormatCtx->streams[i]->codec->codec_type == CODEC_TYPE_VIDEO)
		{
			videoStream = i;
			break;
		}
	if (videoStream == -1)
		return -1; // Didn't find a video stream

	// Get a pointer to the codec context for the video stream
	pCodecCtx = pFormatCtx->streams[videoStream]->codec;

	// Find the decoder for the video stream
	pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
	if (pCodec == NULL)
	{
		fprintf(stderr, "Unsupported codec!\n");
		return -1; // Codec not found
	}
	// Open codec
	if (avcodec_open(pCodecCtx, pCodec) < 0)
		return -1; // Could not open codec

	// Allocate video frame
	pFrame = avcodec_alloc_frame();

	// Allocate an AVFrame structure
	pFrameRGB = avcodec_alloc_frame();
	if (pFrameRGB == NULL)
		return -1;

	// Determine required buffer size and allocate buffer
	numBytes = avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height);
	buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));

	// Assign appropriate parts of buffer to image planes in pFrameRGB
	// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
	// of AVPicture
	avpicture_fill((AVPicture *) pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height);
	struct SwsContext *swsContext;
	swsContext = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width,
			pCodecCtx->height, PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);

	// Read frames and save first five frames to disk
	i = 0;
	while (av_read_frame(pFormatCtx, &packet) >= 0)
	{
		// Is this a packet from the video stream?
		if (packet.stream_index == videoStream)
		{
			// Decode video frame
			avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
			// Did we get a video frame?
			if (frameFinished)
			{
				// Convert the image from its native format to RGB
				sws_scale(swsContext, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data,
						pFrameRGB->linesize);

				// Save the frame to disk
				if (++i <= 5002 && i > 5000)
				{
					//					fprintf(stderr, "保存图片%d\n", i);
					SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);
				}
			}
		}
		// Free the packet that was allocated by av_read_frame
		av_free_packet(&packet);
	}
	fprintf(stderr, "中暑：%d\n", i);
	// Free the RGB image
	av_free(buffer);
	av_free(pFrameRGB);

	// Free the YUV frame
	av_free(pFrame);

	// Close the codec
	avcodec_close(pCodecCtx);

	// Close the video file
	av_close_input_file(pFormatCtx);

	return 0;
}

编译：

gcc demo.c -o demo -lavformat -lavcodec -lswscale  -lavutil  -lz   -lm