本编文章是将之前的解码mp4生成的yuv数据读出来编码生成gif格式的动图, 整体流程和
解码mp4的地址链接:https://www.jianshu.com/p/f4516e6df9f1
1. 主要函数的调用流程
avformat_alloc_output_context2 根据文件名创建视频封装上下文对象
avio_open 打开视频文件
avcodec_find_encoder 查找编码器， 我们使用的是h264,参数就是AV_CODEC_ID_H264
avcodec_alloc_context3 创建编码器的上下文对象并且设置相关参数
avcodec_open2 打开编码器
avformat_new_stream 在视频文件中创建一个视频流对象
avformat_write_header 写入文件头
avfilter_get_by_name获取滤波器
avfilter_inout_alloc 滤波器的输入输出对象
avfilter_graph_alloc 创建一个滤波器图filter graph
avfilter_graph_create_filter 创建滤波器的上下文
av_opt_set_int_list 给滤波器设置参数
avfilter_graph_parse_ptr 设置滤波器图的描述字符串
avfilter_graph_config 检查FilterGraph的配置
av_buffersrc_add_frame_flags 往源滤波器buffer中输入待处理的数据
av_buffersink_get_frame 从滤波器输出端h处理完的数据
avcodec_send_frame 将yuv数据封装成帧并送入编码器
avcodec_receive_packet 从编码器中获取编码好的h264帧
av_interleaved_write_frame 将h264帧写入视频文件中
flush_encoder 写入剩余的帧数据
av_write_trailer 写入文件尾部信息
2. 主要步骤
- 打开新的视频文件
- 创建视频编码器
- 写入文件头
- 初始化滤波器
- 循环将yuv数据帧编码, 写入滤波器的输入端，并从输出端读出， 最后将编码好的帧写入gif文件中
- 写入文件尾部
3.详细代码
void gifEncode() {
char *path = "d:/new_test.gif";
int fps = 25;
//注册组件
av_register_all();
int width = 1920;
int height = 1080;
AVFormatContext* avformat_context = NULL;
//初始化封装格式上下文
avformat_alloc_output_context2(&avformat_context, NULL, NULL, path);
//打开输出文件
if (avio_open(&avformat_context->pb, path, AVIO_FLAG_WRITE) < 0) {
return;
}
//查找编码器
AVCodec * codec = avcodec_find_encoder(AV_CODEC_ID_GIF);
//创建编码器的上下文
AVCodecContext *avcodec_context = avcodec_alloc_context3(codec);
//时间基,pts,dts的时间单位 pts(解码后帧被显示的时间), dts(视频帧送入解码器的时间)的时间单位,是两帧之间的时间间隔
avcodec_context->time_base.den = fps;//pts
avcodec_context->time_base.num = 1;//1秒
avcodec_context->codec_id = AV_CODEC_ID_GIF;
avcodec_context->codec_type = AVMEDIA_TYPE_VIDEO;//表示视频类型
avcodec_context->pix_fmt = AV_PIX_FMT_PAL8;//视频数据像素格式
avcodec_context->width = width;//视频宽高
avcodec_context->height = height;
//在gif文件中
AVStream* avvideo_stream = avformat_new_stream(avformat_context, NULL);//创建一个流
avvideo_stream->codec = avcodec_context;
avvideo_stream->time_base = avcodec_context->time_base;
avvideo_stream->codec->codec_tag = 0;
//初始化编解码器
int ret = avcodec_open2(avcodec_context, codec, nullptr);
if (ret) {
return;
}
int avformat_write_header_result = avformat_write_header(avformat_context, NULL);
if (avformat_write_header_result != AVSTREAM_INIT_IN_WRITE_HEADER) {
return;
}
//这个滤镜字符串的大概意思是设置输入的视频帧格式和fps,然后将帧分成两份o1, o2, 使用palettegen滤镜将o1生成gif调色板p, 最后使用paletteuse滤镜、利用调色板p采样，将o2生成为gif
char *format = "format=pix_fmts=rgb565,fps=%d,split [o1] [o2];[o1] palettegen=stats_mode=diff [p]; [o2] [p] paletteuse=dither=bayer:bayer_scale=5:diff_mode=rectangle";
char *str = (char *)malloc(strlen(format) + 10);
sprintf(str, format, 25);
AVFilterGraph* filter_graph;
AVFilterContext* buffersrc_ctx;
AVFilterContext* buffersink_ctx;
initFilter(avcodec_context, &filter_graph, &buffersrc_ctx, &buffersink_ctx, str);
int buffer_size = av_image_get_buffer_size(avcodec_context->pix_fmt,
avcodec_context->width,
avcodec_context->height,
1);
uint8_t *out_buffer = (uint8_t *)av_malloc(buffer_size);
AVFrame *frame = av_frame_alloc();
AVPacket *av_packet = av_packet_alloc();
av_init_packet(av_packet);
uint8_t * file_buffer = (uint8_t *)av_malloc(width * height * 3 / 2);
FILE *in_file = fopen("d:/yuv4201.yuv", "rb");
int i= 0;
SwsContext * swsContext = sws_getContext(width, height, AV_PIX_FMT_YUV420P, width, height, AV_PIX_FMT_RGB565, SWS_FAST_BILINEAR, NULL, NULL, NULL);
if(swsContext == nullptr){
return;
}
AVFrame *rgbFrame = av_frame_alloc();
rgbFrame->linesize[0] = width * 2;
rgbFrame->format = AV_PIX_FMT_RGB565;
rgbFrame->width = width;
rgbFrame->height = height;
unsigned char * out_buffer1 = (uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_RGB565, avcodec_context->width, avcodec_context->height));
avpicture_fill((AVPicture *)rgbFrame, out_buffer1, AV_PIX_FMT_RGB565, avcodec_context->width, avcodec_context->height);
while (true) {
//读取yuv帧数据 注意yuv420p的长度 width * height * 3 / 2
if (fread(file_buffer, 1, width * height * 3 / 2, in_file) <= 0) {
break;
} else if (feof(in_file)) {
break;
}
//封装yuv帧数据
frame->data[0] = file_buffer;
frame->data[1] = file_buffer + width * height;
frame->data[2] = file_buffer + width * height * 5 / 4;
frame->linesize[0] = width;
frame->linesize[1] = width / 2;
frame->linesize[2] = width / 2;
//frame->pts = i;
frame->pts = i;
frame->width = width;
frame->height = height;
i++;
sws_scale(
swsContext,
(uint8_t const * const *) frame->data,
frame->linesize,
0,
height,
rgbFrame->data,
rgbFrame->linesize
);
rgbFrame->pts = i;
if (i == 1) {
continue;
}
// 往源滤波器buffer中输入待处理的数据
av_buffersrc_add_frame_flags(buffersrc_ctx, rgbFrame, AV_BUFFERSRC_FLAG_KEEP_REF);
}
sws_freeContext(swsContext);
// 最后写入一个空帧
if (av_buffersrc_add_frame_flags(buffersrc_ctx, nullptr, AV_BUFFERSRC_FLAG_KEEP_REF) >= 0) {
do {
AVFrame *gifFrame = av_frame_alloc();
// 从目的滤波器buffersink中输出处理完的数据
int ret = av_buffersink_get_frame(buffersink_ctx, gifFrame);
// ret = av_buffersink_get_frame(buffersink_ctx, filter_frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
// av_log(nullptr, AV_LOG_ERROR, "error get frame from buffer sink %s\n", av_err2str(ret));
break;
}
// write the filter frame to output file
ret = avcodec_send_frame(avcodec_context, gifFrame);
AVPacket *pkt = av_packet_alloc();
av_init_packet(pkt);
while (ret >= 0) {
ret = avcodec_receive_packet(avcodec_context, pkt);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
break;
}
AVRational codecTimebase = avcodec_context->time_base;
AVRational streamTimebase = avformat_context->streams[0]->time_base;
av_packet_rescale_ts(pkt, codecTimebase, streamTimebase);
//pkt.RescaleTs(encoderTimebase, streamTimebase);
av_write_frame(avformat_context, pkt);
}
av_packet_unref(pkt);
} while (ret >= 0);
}
fclose(in_file);
avcodec_close(avcodec_context);
av_free(frame);
av_free(out_buffer);
av_free_packet(av_packet);
av_write_trailer(avformat_context);
avio_close(avformat_context->pb);
avformat_free_context(avformat_context);
avfilter_free(buffersrc_ctx);
avfilter_free(buffersink_ctx);
avfilter_graph_free(&filter_graph);
}
int initFilter(AVCodecContext *context, AVFilterGraph** filter_graph, AVFilterContext** buffersrc_ctx, AVFilterContext** buffersink_ctx, const char* filter_desc)
{
char args[512];
int ret = 0;
//分别获取输入和输出的滤波器
const AVFilter* buffersrc = avfilter_get_by_name("buffer");
const AVFilter* buffersink = avfilter_get_by_name("buffersink");
//创建滤波器的输入端
AVFilterInOut* inputs = avfilter_inout_alloc();
//创建滤波器的输出端
AVFilterInOut* outputs = avfilter_inout_alloc();
//MBAVRational avrational;
//encoder->GetTimeBase(avrational);
enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_PAL8, AV_PIX_FMT_NONE };
// 创建一个滤波器图filter graph
*filter_graph = avfilter_graph_alloc();
if (!outputs || !inputs || !*filter_graph) {
ret = AVERROR(ENOMEM);
return ret;
}
snprintf(args, sizeof(args),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
context->width, context->height, AV_PIX_FMT_RGB565,
context->time_base.num, context->time_base.den,
context->sample_aspect_ratio.num, context->sample_aspect_ratio.den);
//创建滤波器的上下文
ret = avfilter_graph_create_filter(buffersrc_ctx, buffersrc, "in", args, nullptr, *filter_graph);
if (ret < 0) {
av_log(nullptr, AV_LOG_ERROR, "Cannot create buffer source\n");
return ret;
}
ret = avfilter_graph_create_filter(buffersink_ctx, buffersink, "out", nullptr, nullptr, *filter_graph);
if (ret < 0) {
av_log(nullptr, AV_LOG_ERROR, "Cannot create buffer sink\n");
return ret;
}
//给滤波器设置参数
av_opt_set_int_list(*buffersink_ctx, "pix_fmts", pix_fmts, AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
if (ret < 0) {
av_log(nullptr, AV_LOG_ERROR, "can not set output pixel format\n");
return ret;
}
outputs->name = av_strdup("in");
outputs->filter_ctx = *buffersrc_ctx;
outputs->pad_idx = 0;
outputs->next = nullptr;
inputs->name = av_strdup("out");
inputs->filter_ctx = *buffersink_ctx;
inputs->pad_idx = 0;
inputs->next = nullptr;
//设置滤波器图的描述字符串和输入端，输出端
if ((ret = avfilter_graph_parse_ptr(*filter_graph, filter_desc, &inputs, &outputs, nullptr)) < 0) {
av_log(nullptr, AV_LOG_ERROR, "parse filter graph error\n");
return ret;
}
//检查FilterGraph的配置。
if ((ret = avfilter_graph_config(*filter_graph, nullptr)) < 0) {
av_log(nullptr, AV_LOG_ERROR, "config graph error\n");
}
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
return 0;
}
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