FFmpeg———encode_video(学习)

目录

• 前言
• 源码
• 函数
• 最终效果

前言

encode_video:实现了对图片使用指定编码进行编码，生成可播放的视频流，编译时出现了一些错误，做了一些调整。

基本流程：

1、获取指定的编码器

2、编码器内存申请

3、编码器上下文内容参数设置

4、打开编码器

5、申请数据帧内存

6、模拟图片

7、编码

源码

测试代码，做了部分修改

#include <iostream>

using namespace std;


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

extern"C"
{
#include "libavcodec/avcodec.h"
#include "libavutil/opt.h"
#include "libavutil/imgutils.h"
#include "libavutil/error.h"
}

static void encode(AVCodecContext* enc_ctx, AVFrame* frame, AVPacket* pkt,
    FILE* outfile)
{
    int ret;

    /* send the frame to the encoder */
    if (frame)
        printf("Send frame %lld\n", frame->pts);  //修改 lld 替换 PRId64

    /*avcodec_send_frame 与 avcodec_receive_packet 配合使用*/
    ret = avcodec_send_frame(enc_ctx, frame);
    if (ret < 0) {
        fprintf(stderr, "Error sending a frame for encoding\n");
        exit(1);
    }

    while (ret >= 0) {
        ret = avcodec_receive_packet(enc_ctx, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return;
        else if (ret < 0) {
            fprintf(stderr, "Error during encoding\n");
            exit(1);
        }

        printf("Write packet %lld (size=%d)\n", pkt->pts, pkt->size); //修改 lld 替换 PRId64
        fwrite(pkt->data, 1, pkt->size, outfile);
        av_packet_unref(pkt); //清空数据压缩包
    }
}

int main()
{
    const char* filename;
    const AVCodec* codec;
    AVCodecContext* c = NULL;  // 编码器上下文
    int i, ret, x, y;
    FILE* f;
    AVFrame* frame;  // 音视频数据帧结构体
    AVPacket* pkt;
    uint8_t endcode[] = { 0, 0, 1, 0xb7 };

    filename = "text_264";

    /* find the mpeg1video encoder */
    codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

   // 为编码器申请空间并设置初始值
    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    pkt = av_packet_alloc();
    if (!pkt)
        exit(1);

    /* put sample parameters */
    c->bit_rate = 400000;
    /* 分辨率 为2的倍数 */
    c->width = 352;
    c->height = 288;
    /* frames per second */
    c->time_base.num = 1;
    c->time_base.den = 25;

    //帧率
    c->framerate.num = 25;
    c->framerate.den = 1;


    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    c->gop_size = 10;
    c->max_b_frames = 1;  //非B帧之间的最大的B帧数
    c->pix_fmt = AV_PIX_FMT_YUV420P;   //像素格式

    if (codec->id == AV_CODEC_ID_H264)
        av_opt_set(c->priv_data, "preset", "slow", 0);   //设置属性

    /* open it */
    ret = avcodec_open2(c, codec, NULL);
    if (ret < 0) {

        fprintf(stderr, "Could not open codec: %s\n", av_err2str(ret));
        exit(1);
    }

    f = fopen(filename, "wb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", filename);
        exit(1);
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(1);
    }
    frame->format = c->pix_fmt;
    frame->width = c->width;
    frame->height = c->height;

    ret = av_frame_get_buffer(frame, 0);  //申请数据帧缓冲区
    if (ret < 0) {
        fprintf(stderr, "Could not allocate the video frame data\n");
        exit(1);
    }

    /* encode 1 second of video */
    for (i = 0; i < 25; i++) {
        fflush(stdout);

        /* Make sure the frame data is writable.
           On the first round, the frame is fresh from av_frame_get_buffer()
           and therefore we know it is writable.
           But on the next rounds, encode() will have called
           avcodec_send_frame(), and the codec may have kept a reference to
           the frame in its internal structures, that makes the frame
           unwritable.
           av_frame_make_writable() checks that and allocates a new buffer
           for the frame only if necessary.
         */
        ret = av_frame_make_writable(frame);    //确保数据帧是可写
        if (ret < 0)
            exit(1);

        /* 
        模拟图片数据
         */
         /* Y */
        for (y = 0; y < c->height; y++) {
            for (x = 0; x < c->width; x++) {
                frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
            }
        }

        /* Cb and Cr */
        for (y = 0; y < c->height / 2; y++) {
            for (x = 0; x < c->width / 2; x++) {
                frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
                frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
            }
        }

        frame->pts = i;

        /* encode the image */
        encode(c, frame, pkt, f);
    }

    /* flush the encoder */
    encode(c, NULL, pkt, f);

    /* Add sequence end code to have a real MPEG file.
       It makes only sense because this tiny examples writes packets
       directly. This is called "elementary stream" and only works for some
       codecs. To create a valid file, you usually need to write packets
       into a proper file format or protocol; see mux.c.
     */
    if (codec->id == AV_CODEC_ID_MPEG1VIDEO || codec->id == AV_CODEC_ID_MPEG2VIDEO)
        fwrite(endcode, 1, sizeof(endcode), f);
    fclose(f);

    avcodec_free_context(&c);
    av_frame_free(&frame);
    av_packet_free(&pkt);

    return 0;
}

函数

1、int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

向编码器发送音频或视频的数据包与

int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);配合使用

成功返回0

2、av_err2str(errnum)

编译会报错

修改：

char av_error[AV_ERROR_MAX_STRING_SIZE] = { 0 };
#define av_err2str(errnum) \
    av_make_error_string(av_error, AV_ERROR_MAX_STRING_SIZE, errnum)

最终效果