在我的项目中，我想保存 Hevc 文件中的一帧。我在源代码中使用 FFmpeg 来解码 Hevc 文件并获取 AVFrame 和 AVCodecContext。 我需要的是将框架保存为图片（全彩）。
我尝试将其保存为 *.pgm 文件，因此图片只是灰色的，这并不是我真正需要的。
有什么建议吗？谢谢！
void HevcDecoder::Images_Save(char* filename, AVFrame *frame)
{
FILE* file;
int i;
fopen_s(&file, filename, "wb");
fprintf(file, "P5\n%d %d\n%d\n", frame->width, frame->height, 255);
for (i = 0; i < frame->height; i++)
fwrite(frame->data[0] + i * frame->linesize[0], 1, frame->width, file);
fclose(file);
}
void HevcDecoder::Decode(AVCodecContext* dec_ctx, AVFrame* frame, AVPacket* pkt, const char* filename)
{
char buf[1024];
int ret;
ret = avcodec_send_packet(dec_ctx, pkt);
if (ret < 0) {
fprintf(stderr, "Error sending a packet for decoding\n");
exit(1);
}
while (ret >= 0) {
ret = avcodec_receive_frame(dec_ctx, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
return;
else if (ret < 0) {
fprintf(stderr, "Error during decoding\n");
exit(1);
}
printf("saving frame %3d\n", dec_ctx->frame_number);
fflush(stdout);
/* the picture is allocated by the decoder. no need to
free it */
snprintf(buf, sizeof(buf), "%s-%d.pgm", filename, dec_ctx->frame_number);
Images_Save(buf, frame/*, dec_ctx*/);
}
}
使用 FFmpeg CLI 将原始 HEVC 文件转换为图像序列非常简单。
Assume input.265是输入文件（原始 HEVC 视频流）：
转换为 PNG 图像：
ffmpeg -i input.265 %05d.png
转换为 PPM 图像：
ffmpeg -i input.265 %05d.ppm
如果输入视频使用 MP4 容器并且您想要 JPEG 图像：
ffmpeg -i input.265 %05d.jpg
使用 FFmpeg C 接口（Libav）：
为了使事情可重现，首先使用 FFmpeg CLI 创建输入视频文件：
ffmpeg -y -f lavfi -i testsrc=size=192x108:rate=1:duration=10 -vcodec libx265 -pix_fmt yuv420p input.265
上述命令创建 HEVC (H.265) 编码流 - 10 帧，分辨率为 192x108，像素格式为 YUV420（合成模式）。
编码流是原始视频流（没有容器）。
Note:
将图像保存为彩色图像：
该代码示例重用了来自这个帖子 https://stackoverflow.com/questions/71363536/avcodec-not-able-to-decode-hevc.
我们可以使用以下代码示例这个帖子 https://stackoverflow.com/questions/69442603/ffmpeg-convert-ycbcr-to-rgb-using-sws-scale
这是代码示例：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
extern "C" {
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}
#define INBUF_SIZE 1024
//static void pgm_save(unsigned char* buf, int wrap, int xsize, int ysize, char* filename)
//{
// FILE* f;
// int i;
//
// f = fopen(filename, "wb");
// fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
// for (i = 0; i < ysize; i++)
// fwrite(buf + i * wrap, 1, xsize, f);
// fclose(f);
//}
//Save RGB image as PPM file format
static void ppm_save(unsigned char* buf, int wrap, int xsize, int ysize, char* filename)
{
FILE* f;
int i;
f = fopen(filename, "wb");
fprintf(f, "P6\n%d %d\n%d\n", xsize, ysize, 255);
for (i = 0; i < ysize; i++)
{
fwrite(buf + i * wrap, 1, xsize*3, f);
}
fclose(f);
}
static void decode(AVCodecContext* dec_ctx, AVFrame* frame, AVPacket* pkt, const char* filename)
{
struct SwsContext* sws_ctx = NULL;
char buf[1024];
int ret;
int sts;
ret = avcodec_send_packet(dec_ctx, pkt);
if (ret < 0)
{
fprintf(stderr, "Error sending a packet for decoding\n");
exit(1);
}
//Create SWS Context for converting from decode pixel format (like YUV420) to RGB
////////////////////////////////////////////////////////////////////////////
sws_ctx = sws_getContext(dec_ctx->width,
dec_ctx->height,
dec_ctx->pix_fmt,
dec_ctx->width,
dec_ctx->height,
AV_PIX_FMT_RGB24,
SWS_BICUBIC,
NULL,
NULL,
NULL);
if (sws_ctx == nullptr)
{
return; //Error!
}
////////////////////////////////////////////////////////////////////////////
//Allocate frame for storing image converted to RGB.
////////////////////////////////////////////////////////////////////////////
AVFrame* pRGBFrame = av_frame_alloc();
pRGBFrame->format = AV_PIX_FMT_RGB24;
pRGBFrame->width = dec_ctx->width;
pRGBFrame->height = dec_ctx->height;
sts = av_frame_get_buffer(pRGBFrame, 0);
if (sts < 0)
{
return; //Error!
}
////////////////////////////////////////////////////////////////////////////
while (ret >= 0)
{
ret = avcodec_receive_frame(dec_ctx, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
{
return;
}
else if (ret < 0)
{
fprintf(stderr, "Error during decoding\n");
exit(1);
}
printf("saving frame %3d\n", dec_ctx->frame_number);
fflush(stdout);
/* the picture is allocated by the decoder. no need to
free it */
//snprintf(buf, sizeof(buf), "%s_%03d.pgm", filename, dec_ctx->frame_number);
//pgm_save(frame->data[0], frame->linesize[0],
// frame->width, frame->height, buf);
//Convert from input format (e.g YUV420) to RGB and save to PPM:
////////////////////////////////////////////////////////////////////////////
sts = sws_scale(sws_ctx, //struct SwsContext* c,
frame->data, //const uint8_t* const srcSlice[],
frame->linesize, //const int srcStride[],
0, //int srcSliceY,
frame->height, //int srcSliceH,
pRGBFrame->data, //uint8_t* const dst[],
pRGBFrame->linesize); //const int dstStride[]);
if (sts != frame->height)
{
return; //Error!
}
snprintf(buf, sizeof(buf), "%s_%03d.ppm", filename, dec_ctx->frame_number);
ppm_save(pRGBFrame->data[0], pRGBFrame->linesize[0], pRGBFrame->width, pRGBFrame->height, buf);
////////////////////////////////////////////////////////////////////////////
}
//Free
sws_freeContext(sws_ctx);
av_frame_free(&pRGBFrame);
}
int main(int argc, char** argv)
{
const char* filename, * outfilename;
const AVCodec* codec;
AVCodecParserContext* parser;
AVCodecContext* c = NULL;
FILE* f;
AVFrame* frame;
uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
uint8_t* data;
size_t data_size;
int ret;
AVPacket* pkt;
filename = argv[1];
outfilename = argv[2];
pkt = av_packet_alloc();
if (!pkt)
{
exit(1);
}
//memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
memset(inbuf, 0, sizeof(inbuf));
codec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
if (!codec)
{
fprintf(stderr, "Codec not found\n");
exit(1);
}
parser = av_parser_init(codec->id);
if (!parser)
{
fprintf(stderr, "parser not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c)
{
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
if (avcodec_open2(c, codec, NULL) < 0)
{
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "rb");
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);
}
while (!feof(f))
{
/* read raw data from the input file */
data_size = fread(inbuf, 1, INBUF_SIZE, f);
if (!data_size)
{
break;
}
/* use the parser to split the data into frames */
data = inbuf;
while (data_size > 0)
{
ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size, data, (int)data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if (ret < 0)
{
fprintf(stderr, "Error while parsing\n");
exit(1);
}
data += ret;
data_size -= ret;
if (pkt->data)
{
printf("NICE\n");
decode(c, frame, pkt, outfilename);
}
}
}
/* flush the decoder */
decode(c, frame, NULL, outfilename);
fclose(f);
av_parser_close(parser);
avcodec_free_context(&c);
av_frame_free(&frame);
av_packet_free(&pkt);
return 0;
}
使用 OpenCV 显示图像：
显示图像最简单的方法之一是使用OpenCV https://opencv.org/图书馆。
首次设置同时使用 FFmpeg 和 OpenCV 的项目可能具有挑战性。
cv::imshow其次是cv::waitKey.代码示例：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//Use OpenCV for showing the inage
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
extern "C" {
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}
#define INBUF_SIZE 1024
//static void pgm_save(unsigned char* buf, int wrap, int xsize, int ysize, char* filename)
//{
// FILE* f;
// int i;
//
// f = fopen(filename, "wb");
// fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
// for (i = 0; i < ysize; i++)
// fwrite(buf + i * wrap, 1, xsize, f);
// fclose(f);
//}
//Save RGB image as PPM file format
//static void ppm_save(unsigned char* buf, int wrap, int xsize, int ysize, char* filename)
//{
// FILE* f;
// int i;
//
// f = fopen(filename, "wb");
// fprintf(f, "P6\n%d %d\n%d\n", xsize, ysize, 255);
//
// for (i = 0; i < ysize; i++)
// {
// fwrite(buf + i * wrap, 1, xsize*3, f);
// }
//
// fclose(f);
//}
static void decode(AVCodecContext* dec_ctx, AVFrame* frame, AVPacket* pkt, const char* filename)
{
struct SwsContext* sws_ctx = NULL;
char filename_buf[1024];
int ret;
int sts;
ret = avcodec_send_packet(dec_ctx, pkt);
if (ret < 0)
{
fprintf(stderr, "Error sending a packet for decoding\n");
exit(1);
}
//Create SWS Context for converting from decode pixel format (like YUV420) to BGR
////////////////////////////////////////////////////////////////////////////
sws_ctx = sws_getContext(dec_ctx->width,
dec_ctx->height,
dec_ctx->pix_fmt,
dec_ctx->width,
dec_ctx->height,
AV_PIX_FMT_BGR24, //For OpenCV, we want BGR pixel format.
SWS_BICUBIC,
NULL,
NULL,
NULL);
if (sws_ctx == nullptr)
{
return; //Error!
}
////////////////////////////////////////////////////////////////////////////
//Allocate frame for storing image converted to RGB.
////////////////////////////////////////////////////////////////////////////
AVFrame* pBGRFrame = av_frame_alloc();
pBGRFrame->format = AV_PIX_FMT_BGR24;
pBGRFrame->width = dec_ctx->width;
pBGRFrame->height = dec_ctx->height;
sts = av_frame_get_buffer(pBGRFrame, 0);
if (sts < 0)
{
return; //Error!
}
////////////////////////////////////////////////////////////////////////////
while (ret >= 0)
{
ret = avcodec_receive_frame(dec_ctx, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
{
return;
}
else if (ret < 0)
{
fprintf(stderr, "Error during decoding\n");
exit(1);
}
printf("saving frame %3d\n", dec_ctx->frame_number);
fflush(stdout);
/* the picture is allocated by the decoder. no need to
free it */
//snprintf(buf, sizeof(buf), "%s_%03d.pgm", filename, dec_ctx->frame_number);
//pgm_save(frame->data[0], frame->linesize[0],
// frame->width, frame->height, buf);
//Convert from input format (e.g YUV420) to BGR:
////////////////////////////////////////////////////////////////////////////
sts = sws_scale(sws_ctx, //struct SwsContext* c,
frame->data, //const uint8_t* const srcSlice[],
frame->linesize, //const int srcStride[],
0, //int srcSliceY,
frame->height, //int srcSliceH,
pBGRFrame->data, //uint8_t* const dst[],
pBGRFrame->linesize); //const int dstStride[]);
if (sts != frame->height)
{
return; //Error!
}
snprintf(filename_buf, sizeof(filename_buf), "%s_%03d.jpg", filename, dec_ctx->frame_number);
//ppm_save(pBGRFrame->data[0], pBGRFrame->linesize[0], pBGRFrame->width, pBGRFrame->height, buf);
////////////////////////////////////////////////////////////////////////////
//Use OpenCV for showing the image (and save the image in JPEG format):
////////////////////////////////////////////////////////////////////////////
cv::Mat img = cv::Mat(pBGRFrame->height, pBGRFrame->width, CV_8UC3, pBGRFrame->data[0], pBGRFrame->linesize[0]); //cv::Mat is OpenCV "thin image wrapper".
cv::imshow("img", img);
cv::waitKey(100); //Wait 100msec (relativly long time - for testing).
//Save the inage in JPEG format using OpenCV
cv::imwrite(filename_buf, img);
////////////////////////////////////////////////////////////////////////////
}
//Free
sws_freeContext(sws_ctx);
av_frame_free(&pBGRFrame);
}
int main(int argc, char** argv)
{
const char* filename, * outfilename;
const AVCodec* codec;
AVCodecParserContext* parser;
AVCodecContext* c = NULL;
FILE* f;
AVFrame* frame;
uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
uint8_t* data;
size_t data_size;
int ret;
AVPacket* pkt;
filename = argv[1];
outfilename = argv[2];
pkt = av_packet_alloc();
if (!pkt)
{
exit(1);
}
//memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
memset(inbuf, 0, sizeof(inbuf));
codec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
if (!codec)
{
fprintf(stderr, "Codec not found\n");
exit(1);
}
parser = av_parser_init(codec->id);
if (!parser)
{
fprintf(stderr, "parser not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c)
{
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
if (avcodec_open2(c, codec, NULL) < 0)
{
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "rb");
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);
}
while (!feof(f))
{
/* read raw data from the input file */
data_size = fread(inbuf, 1, INBUF_SIZE, f);
if (!data_size)
{
break;
}
/* use the parser to split the data into frames */
data = inbuf;
while (data_size > 0)
{
ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size, data, (int)data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if (ret < 0)
{
fprintf(stderr, "Error while parsing\n");
exit(1);
}
data += ret;
data_size -= ret;
if (pkt->data)
{
printf("NICE\n");
decode(c, frame, pkt, outfilename);
}
}
}
/* flush the decoder */
decode(c, frame, NULL, outfilename);
fclose(f);
av_parser_close(parser);
avcodec_free_context(&c);
av_frame_free(&frame);
av_packet_free(&pkt);
return 0;
}
示例输出：
output_001.jpg:
output_002.jpg:
output_003.jpg:
