Ffmpeg video coding

1. brief introduction

Encoded video data , As shown in the figure below , Will be original YUV The data is encoded as H.264 perhaps H.265.

 

2. technological process

 

2.1 In the use of FFmpeg API Before , Need to register first API, And then you can use it API. Of course , The new version of the library does not need to call the following methods .

av_register_all()

2.2 Find the encoder , This example demonstrates coding H.264

    AVCodec* codec = nullptr;

	// Find the encoder 
	codec = avcodec_find_encoder(AV_CODEC_ID_H264);
	if (!codec) 
	{
		fprintf(stderr, "Codec not found\n");
		exit(1);
	}

2.3 apply AVCodecContext

    // apply AVCodecContext
    AVCodecContext* codec_ctx = nullptr;
	codec_ctx = avcodec_alloc_context3(codec);
	if (!codec_ctx)
	{
		fprintf(stderr, "Could not allocate audio codec context\n");
		exit(1);
	}

2.4 Set video parameters

For example, set the width of the video 、 high 、fps、 Bit rate and so on

	codec_ctx->bit_rate = 2581504;	// Bit rate   Clarity related 
	codec_ctx->width = 1920;
	codec_ctx->height = 1012;

	AVRational time_base = { 1, 25 };
	AVRational framerate = { 25, 1 };

	codec_ctx->time_base = time_base;
	codec_ctx->framerate = framerate;
	codec_ctx->gop_size = 10;
	codec_ctx->max_b_frames = 1;
	codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;

2.5 Turn on the encoder

	// Turn on the encoder 
	if (avcodec_open2(codec_ctx, codec, NULL) < 0)
	{
		fprintf(stderr, "Could not open codec\n");
		exit(1);
	}

2.6 Set the parameters of the video frame

Format 、 wide 、 higher .

	AVFrame *frame = av_frame_alloc();
	if (!frame) 
	{
		fprintf(stderr, "Could not allocate audio frame\n");
		exit(1);
	}

	frame->format = codec_ctx->pix_fmt;
	frame->width = codec_ctx->width;
	frame->height = codec_ctx->height;

2.7 by frame Allocate space

	/* allocate the data buffers */
	int ret = av_frame_get_buffer(frame, 0);
	if (ret < 0) 
	{
		fprintf(stderr, "Could not allocate audio data buffers\n");
		exit(1);
	}

2.8 obtain frame Of buffer size , Allocate one buffer

	int bufferSize = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, 
                frame->width, frame->height, 1);
	uint8_t* buffer = (uint8_t*)av_malloc(bufferSize);

2.9 take frame The data pointer of points to the applied buffer, Later, you only need to operate buffer That's it .

	ret = av_image_fill_arrays(frame->data, frame->linesize, 
                    buffer, AV_PIX_FMT_YUV420P, 1920, 1012, 1);
	if (ret < 0)
	{
		exit(1);
	}

2.10 Reading data , Start coding

	// Open the output file 
	char fileName[20] = "output.h264";
	FILE* f = fopen(fileName, "wb");
	if (!f)
	{
		fprintf(stderr, "Could not open %s\n", fileName);
		exit(1);
	}


    // Open the input file 
	char inputFile[20] = {0};

	for(int i=1;i<256;i++)
	{
		sprintf(inputFile, "img/%d.yuv", i);

		FILE* fp = fopen(inputFile, "rb");
		if (!fp)
		{
			fprintf(stderr, "Could not open %s\n", inputFile);
			exit(1);
		}

		// Read data from file 
		int count = fread(buffer, sizeof(char), bufferSize, fp);

		fclose(fp);

		frame->pts = i;
	
		// Start coding 
		ret = avcodec_send_frame(codec_ctx, frame);

		while (ret >= 0)
		{
			ret = avcodec_receive_packet(codec_ctx, pkt);
			if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
			{
				break;
			}
			else if (ret < 0)
			{
				break;
			}

			
			// The encoded data is written to the local file 
			fwrite(pkt->data, 1, pkt->size, f);
			av_packet_unref(pkt);
		}
	}

	fclose(f);

3. The video is decoded as YUV

I will H.264 After decoding the data of , Saved hundreds of frames YUV Data to local .

FFmpeg Video decoding （ Seconds understand ）_Mr.codeee The blog of -CSDN Blog

4. Source code

take 3 Hundreds of frames in YUV Data is encoded to get H.264.

#include "pch.h"
#include <iostream>

extern "C"
{
#include "libavformat/avformat.h"
#include "libavutil/dict.h"
#include "libavutil/opt.h"
#include "libavutil/timestamp.h"
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"
#include "libavutil/imgutils.h" 
};


int main()
{
	//av_register_all();
	avformat_network_init();

    AVCodec* codec = nullptr;

	// Find the encoder 
	codec = avcodec_find_encoder(AV_CODEC_ID_H264);
	if (!codec) 
	{
		fprintf(stderr, "Codec not found\n");
		exit(1);
	}

    // apply AVCodecContext
    AVCodecContext* codec_ctx = nullptr;
	codec_ctx = avcodec_alloc_context3(codec);
	if (!codec_ctx)
	{
		fprintf(stderr, "Could not allocate audio codec context\n");
		exit(1);
	}

	codec_ctx->bit_rate = 2581504;	// Bit rate   Clarity related 
	codec_ctx->width = 1920;
	codec_ctx->height = 1012;

	AVRational time_base = { 1, 25 };
	AVRational framerate = { 25, 1 };

	codec_ctx->time_base = time_base;
	codec_ctx->framerate = framerate;
	codec_ctx->gop_size = 10;
	codec_ctx->max_b_frames = 1;
	codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;

	// Turn on the encoder 
	if (avcodec_open2(codec_ctx, codec, NULL) < 0)
	{
		fprintf(stderr, "Could not open codec\n");
		exit(1);
	}

	AVPacket *pkt = av_packet_alloc();
	if (!pkt)
	{
		fprintf(stderr, "could not allocate the packet\n");
		exit(1);
	}

	AVFrame *frame = av_frame_alloc();
	if (!frame) 
	{
		fprintf(stderr, "Could not allocate audio frame\n");
		exit(1);
	}

	frame->format = codec_ctx->pix_fmt;
	frame->width = codec_ctx->width;
	frame->height = codec_ctx->height;

	/* allocate the data buffers */
	int ret = av_frame_get_buffer(frame, 0);
	if (ret < 0) 
	{
		fprintf(stderr, "Could not allocate audio data buffers\n");
		exit(1);
	}

	// Open the output file 
	char fileName[20] = "output.h264";
	FILE* f = fopen(fileName, "wb");
	if (!f)
	{
		fprintf(stderr, "Could not open %s\n", fileName);
		exit(1);
	}

	int bufferSize = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, frame->width, frame->height, 1);
	uint8_t* buffer = (uint8_t*)av_malloc(bufferSize);

	ret = av_image_fill_arrays(frame->data, frame->linesize, buffer, AV_PIX_FMT_YUV420P, 1920, 1012, 1);
	if (ret < 0)
	{
		exit(1);
	}

	// Open the input file 
	char inputFile[20] = {0};

	for(int i=1;i<256;i++)
	{
		sprintf(inputFile, "img/%d.yuv", i);

		FILE* fp = fopen(inputFile, "rb");
		if (!fp)
		{
			fprintf(stderr, "Could not open %s\n", inputFile);
			exit(1);
		}

		// Read data from file 
		int count = fread(buffer, sizeof(char), bufferSize, fp);

		fclose(fp);

		frame->pts = i;
	
		// Start coding 
		ret = avcodec_send_frame(codec_ctx, frame);

		while (ret >= 0)
		{
			ret = avcodec_receive_packet(codec_ctx, pkt);
			if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
			{
				break;
			}
			else if (ret < 0)
			{
				break;
			}

			
			// The encoded data is written to the local file 
			fwrite(pkt->data, 1, pkt->size, f);
			av_packet_unref(pkt);
		}
	}

	fclose(f);

	av_free(buffer);
	avcodec_close(codec_ctx);
	avcodec_free_context(&codec_ctx);
	av_frame_free(&frame);
	av_packet_free(&pkt);


    return 0;
}