FFMPEG内存操作（二）从内存中读取数及数据格式的转换

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在雷神的《最简单的基于FFmpeg的内存读写例子（内存播放器）》中，它是设计回调函数从输入文件中读取数据。与FFMPEG 官方给出的avio_reading.c不同的是，雷神给的例子是当需要数据的时候，回调函数才去从输入文件读取数据，而avio_reading.c 则是直接全部数据读取到内存中待后面处理。

在我的这个实例中，我是将读取到的输入文件解码成YUV420P数据格式。同时可以通过设置不同的数据格式和尺寸实现输出图像的拉伸缩小或是数据格式的装换。

/*=============================================================================
# FileName: ffmpeg_mem_read.c
# Desc: an example of ffmpeg read from memory
# Author: licaibiao
# LastChange: 2017-03-21
=============================================================================*/
#include <stdio.h>
#define __STDC_CONSTANT_MACROS
#include "avcodec.h"
#include "avformat.h"
#include "swscale.h"
//#define QUARTER_SHOW
charchar *input_name = "cuc60anniversary_start.ts";
FILEFILE *fp_open = NULL;
int read_buffer(voidvoid *opaque, uint8_t *buf, int buf_size){
if(!feof(fp_open)){
int true_size=fread(buf,1,buf_size,fp_open);
return true_size;
}else{
return -1;
}
}
int main(int argc, char* argv[])
{
AVFormatContext *pFormatCtx;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
AVIOContext *avio;
AVFrame *pFrame;
AVFrame *pFrameYUV;
AVPacket *packet;
struct SwsContext *img_convert_ctx;
int videoindex;
int i;
int ret;
int got_picture;
int y_size;
unsigned char *aviobuffer;
FILE *fp_yuv;
//fp_open = fopen(argv[1],"rb+");
fp_open = fopen(input_name, "rb+");
fp_yuv = fopen("output.yuv", "wb+");
av_register_all();
pFormatCtx = avformat_alloc_context();
aviobuffer=(unsigned charchar *)av_malloc(32768);
avio = avio_alloc_context(aviobuffer, 32768,0,NULL,read_buffer,NULL,NULL);
/* Open an input stream and read the header. */
pFormatCtx->pb = avio;
if(avformat_open_input(&pFormatCtx,NULL,NULL,NULL)!=0){
printf("Couldn't open input stream.\n");
return -1;
}
/* Read packets of a media file to get stream information. */
if(avformat_find_stream_info(pFormatCtx,NULL)<0){
printf("Couldn't find stream information.\n");
return -1;
}
videoindex = -1;
for(i=0; i<pFormatCtx->nb_streams; i++) {
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
videoindex=i;
break;
}
}
if(videoindex==-1){
printf("Didn't find a video stream.\n");
return -1;
}
av_dump_format(pFormatCtx, 0, input_name, 0);
/* Find a registered decoder with a matching codec ID */
pCodecCtx = pFormatCtx->streams[videoindex]->codec;
pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL){
printf("Codec not found.\n");
return -1;
}
/* Initialize the AVCodecContext to use the given AVCodec */
if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
printf("Could not open codec.\n");
return -1;
}
pFrame = av_frame_alloc();
pFrameYUV = av_frame_alloc();
uint8_t *out_buffer=(uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
/* Allocate and return an SwsContext. */
/* srcW：源图像的宽
* srcH：源图像的高
* srcFormat：源图像的像素格式
* dstW：目标图像的宽
* dstH：目标图像的高
* dstFormat：目标图像的像素格式
* flags：设定图像拉伸使用的算法
*/
#ifndef QUARTER_SHOW
img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
#else
img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width/2, pCodecCtx->height/2, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
printf("out frame width = %d, height = %d \n", pCodecCtx->width/2,pCodecCtx->height/2);
#endif
packet = (AVPacket *)av_malloc(sizeof(AVPacket));
while(av_read_frame(pFormatCtx, packet) >= 0){
if(packet->stream_index == videoindex){
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if(ret < 0){
printf("Decode Error.\n");
return -1;
}
if(got_picture){
/* Scale the image slice in srcSlice and put the resulting scaled slice in the image in dst. 图像处理函数 */
/* c the scaling context previously created with sws_getContext()
* srcSlice the array containing the pointers to the planes of the source slice
* srcStride the array containing the strides for each plane of
* srcSliceY the position in the source image of the slice to process, that is the number (counted starting from
zero) in the image of the first row of the slice 输入图像数据的第多少列开始逐行扫描，通常设为0
* srcSliceH the height of the source slice, that is the number of rows in the slice 为需要扫描多少行，通常为输入图像数据的高度
* dst the array containing the pointers to the planes of the destination image
* dstStride the array containing the strides for each plane of the destination image
*/
sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
#ifndef QUARTER_SHOW
// printf("pFrameYUV->height = %d\n ",pFrameYUV->height);
// printf("pFrameYUV->width = %d\n ", pFrameYUV->width);
// printf("pFrameYUV->pkt_size = %d\n ",pFrameYUV->pkt_size);
y_size = pCodecCtx->width*pCodecCtx->height;
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
#else
for(i=0; i<pCodecCtx->height/2; i++){
fwrite(pFrameYUV->data[0]+pCodecCtx->width * i ,1,pCodecCtx->width/2,fp_yuv);
}
for(i=0; i<pCodecCtx->height/2; i = i + 2){
fwrite(pFrameYUV->data[1]+pCodecCtx->width * i/4 ,1,pCodecCtx->width/4,fp_yuv);
}
for(i=0; i<pCodecCtx->height/2; i = i + 2 ){
fwrite(pFrameYUV->data[2]+pCodecCtx->width * i/4 ,1,pCodecCtx->width/4,fp_yuv);
}
#endif
}
}
av_free_packet(packet);
}
sws_freeContext(img_convert_ctx);
fclose(fp_yuv);
fclose(fp_open);
av_free(out_buffer);
av_free(pFrameYUV);
avcodec_close(pCodecCtx);
avformat_close_input(&pFormatCtx);
return 0;
}