03_avcodec_context..cpp

#include <stdio.h>


extern "C"
{
	// include format and codec headers
#include <libavformat\avformat.h>
#include <libavcodec\avcodec.h>

}


int main()
{
	
	// declare format and codec contexts, also codec for decoding
	AVFormatContext *fmt_ctx = NULL;
	AVCodecContext *CodecCtx = NULL;
	AVCodec *Codec = NULL;
	int ret;
	char *filename = "D:\\Wildlife.wmv";
	int VideoStreamID = -1;


	av_register_all();

	// open input file
	if (ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL) < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "cannot open input file\n");	
		goto end;
	}
		
	//get stream info
	if (ret = avformat_find_stream_info(fmt_ctx, NULL) < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "cannot get stream info\n");
		goto end;
	}
		
	// get video stream index
	for (int i = 0; i < fmt_ctx->nb_streams; i++)
	{
		if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
		{
			VideoStreamID = i;
			break;
		}
	}

	if (VideoStreamID < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "No video stream\n");
		goto end;
	}

	// dump video stream info
	av_dump_format(fmt_ctx, VideoStreamID, filename, false);

	//alloc memory for codec context
	CodecCtx = avcodec_alloc_context3(NULL);

	// retrieve codec params from format context
	if (ret = avcodec_parameters_to_context(CodecCtx, fmt_ctx->streams[VideoStreamID]->codecpar) < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "Cannot get codec parameters\n");
		goto end;
	}
		
	// find decoding codec
	Codec = avcodec_find_decoder(CodecCtx->codec_id);

	if (Codec == NULL)
	{
		av_log(NULL, AV_LOG_ERROR, "No decoder found\n");
		goto end;
	}

	// try to open codec
	if (ret = avcodec_open2(CodecCtx, Codec, NULL) < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
		goto end;
	}

	printf("\nDecoding codec is : %s\n", Codec->name);


	// clear and out
	end:
	if (CodecCtx)
		avcodec_close(CodecCtx);
	if (fmt_ctx)
		avformat_close_input(&fmt_ctx);	
	system("PAUSE");

	return 0;
}