ffmpeg解码JPG和PNG等图片 2013-05-15 09:50:22 分类： 嵌入式 【特别提醒：本文写作时，贴上去的代码，"\n"回车符号的"\"没有了，不知道为啥，所以阅读代码时

ffmpeg解码JPG和PNG等图片 2013-05-15
09:50:22

分类： 嵌入式

【特别提醒：本文写作时，贴上去的代码，"\n"回车符号的"\"没有了，不知道为啥，所以阅读代码时请注意区分，或者欢迎到我的CSDN网站阅读

http://blog.csdn.net/jgf_ntu/article/details/8928977】

一般我们都是用ffmpeg来解码音视频，如果是JPG和PNG等图片呢，其实跟解码视频是一样的，因为视频也是一幅一幅的图片进行解码的，只不过视频的帧是会前后参考的，而JPG等图片来讲，就是独立的一帧而已。

那么，我们参考之前的一篇文章http://blog.chinaunix.net/uid-25272011-id-3633434.html 【一段ffmpeg视频解码为YUV420P的示例代码】 ，稍作修改即可来演示。

同时为了能够保存解码后的图片，我们还需要了解一些YUV或者RGB等各种格式的数据的内存存储方式，这些知识可以参照我之前的另一篇文章《YUV420格式解析》 ，这里详细描述了各种格式的空间存储机制。

一般解码视频时，我们在调用ffmpeg进行解码时，生成的格式一般都是YUV420P的，但解码图皮时可能会有各种形式，如YUVJ422P、YUVJ444P、RGB24等等，本文没有采用ffmpeg的sws_scale函数做统一的转

换，为的是记录如何来存储这些解码后的图片。

先给出如何从ffmpeg的Frame结构体中保存上述的四种解码后的数据：

点击(此处)折叠或打开

/**

* save yuv420p frame [YUV]

*/

void yuv420p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)

{

int i = 0;

int width = pCodecCtx->width, height = pCodecCtx->height;

int height_half = height / 2, width_half = width / 2;

int y_wrap = pFrame->linesize[0];

int u_wrap = pFrame->linesize[1];

int v_wrap = pFrame->linesize[2];

unsigned char *y_buf = pFrame->data[0];

unsigned char *u_buf = pFrame->data[1];

unsigned char *v_buf = pFrame->data[2];

//save
y

for (i = 0; i < height; i++)

fwrite(y_buf + i * y_wrap, 1, width, pfout);

fprintf(stderr, "===>save
Y successn");

//save
u

for (i = 0; i < height_half; i++)

fwrite(u_buf + i * u_wrap, 1, width_half, pfout);

fprintf(stderr, "===>save
U successn");

//save
v

for (i = 0; i < height_half; i++)

fwrite(v_buf + i * v_wrap, 1, width_half, pfout);

fprintf(stderr, "===>save
V successn");

fflush(pfout);

}

/**

* save yuv422p frame [YUV]

*/

void yuv422p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)

{

int i = 0;

int width = pCodecCtx->width, height = pCodecCtx->height;

int height_half = height / 2, width_half = width / 2;

int y_wrap = pFrame->linesize[0];

int u_wrap = pFrame->linesize[1];

int v_wrap = pFrame->linesize[2];

unsigned char *y_buf = pFrame->data[0];

unsigned char *u_buf = pFrame->data[1];

unsigned char *v_buf = pFrame->data[2];

//save
y

for (i = 0; i < height; i++)

fwrite(y_buf + i * y_wrap, 1, width, pfout);

fprintf(stderr, "===>save
Y successn");

//save
u

for (i = 0; i < height; i++)

fwrite(u_buf + i * u_wrap, 1, width_half, pfout);

fprintf(stderr, "===>save
U successn");

//save
v

for (i = 0; i < height; i++)

fwrite(v_buf + i * v_wrap, 1, width_half, pfout);

fprintf(stderr, "===>save
V successn");

fflush(pfout);

}

/**

* save rgb24 frame [PPM]

*/

void rgb24_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)

{

int i = 0;

int width = pCodecCtx->width, height = pCodecCtx->height;

/* write
PPM header */

fprintf(pfout, "P6n%d
%dn255n", width, height);

/* write
pixel data */

for(i =0; i < height; i++)

fwrite(pFrame->data[0] + i * pFrame->linesize[0], 1, width * 3, pfout);

fflush(pfout);

}

/**

* save yuv444p frame [YUV]

*/

void yuv444p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)

{

int i = 0;

int width = pCodecCtx->width, height = pCodecCtx->height;

int y_wrap = pFrame->linesize[0];

int u_wrap = pFrame->linesize[1];

int v_wrap = pFrame->linesize[2];

unsigned char *y_buf = pFrame->data[0];

unsigned char *u_buf = pFrame->data[1];

unsigned char *v_buf = pFrame->data[2];

//save
y

for (i = 0; i < height; i++)

fwrite(y_buf + i * y_wrap, 1, width, pfout);

fprintf(stderr, "===>save
Y successn");

//save
u

for (i = 0; i < height; i++)

fwrite(u_buf + i * u_wrap, 1, width, pfout);

fprintf(stderr, "===>save
U successn");

//save
v

for (i = 0; i < height; i++)

fwrite(v_buf + i * v_wrap, 1, width, pfout);

fprintf(stderr, "===>save
V successn");

fflush(pfout);

}

可以对照各种格式看一下代码，应该是很好理解的，下面是其余的main代码，可以编译运行

点击(此处)折叠或打开

/**

* decode picture by ffmpeg-1.0 for jpg and png ...

*

* 2013-05-14

* juguofeng<jgfntu@gmail.com>

*/

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <libavcodec/avcodec.h>

#include <libavformat/avformat.h>

FILE *pfout = NULL;

char ffrvout[128] = { 0 };

/* how many yuv pic you want to save */

#define FRAME_NUM 1

/* enable video demux data save to file */

//#define
ENABLE_DEMUX_SAVE

/* enable yuv pic save to file */

#define ENABLE_YUV_SAVE

/* enable print each video
bytes */

#define ENABLE_PRINT_FRAME_BYTES

/* how many bytes you want to print */

#define PRINT_BYTES 30

/**

* main thread

*/

int main(int argc, char *argv[])

{

int i;

char szFileName[128] = {0};

int decLen = 0;

int frame = 0;

AVCodecContext *pCodecCtx = NULL;

AVFrame *pFrame = NULL;

AVCodec *pCodec = NULL;

AVFormatContext *pFormatCtx = NULL;

if(argc != 3)

{

fprintf(stderr, "ERROR:need
3 argument!n");

exit(-1);

}

sprintf(szFileName, "%s", argv[1]);

#ifdef ENABLE_DEMUX_SAVE

FILE* frvdemux = fopen("rvdemuxout.rm","wb+");

if (NULL == frvdemux)

{

fprintf(stderr, "create
rvdemuxout file failedn");

exit(1);

}

#endif

/* output
yuv file name */

sprintf(ffrvout, "%s", argv[2]);

pfout = fopen(ffrvout, "wb+");

if (NULL == pfout)

{

printf("create output
file failedn");

exit(1);

}

printf("==========> Begin
test ffmpeg call ffmpeg rv decodern");

av_register_all();

/* Open
input video file */

//printf("before
avformat_open_input [%s]n", szFileName);

if(avformat_open_input(&pFormatCtx, szFileName, NULL, NULL)!= 0)

{

fprintf(stderr, "Couldn't
open input filen");

return -1;

}

//printf("after
avformat_open_inputn");

/* Retrieve
stream information */

if(av_find_stream_info(pFormatCtx) < 0)

{

printf("av_find_stream_info
ERRORn");

return -1;

}

//printf("after
av_find_stream_info, n");

/* Find
the first video stream */

int videoStream = -1;

printf("==========> pFormatCtx->nb_streams
= %dn", pFormatCtx->nb_streams);

for(i = 0; i < pFormatCtx->nb_streams; i++) {

if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {

videoStream = i;

printf("the first
video stream index: videoStream = %dn",videoStream);

break;

}

}

if(videoStream == -1)

return -1; // Didn't
find a video stream

/* Get a
pointer to the codec context for the
video stream */

pCodecCtx = pFormatCtx->streams[videoStream]->codec;

printf("pCodecCtx->codec_id
= %dn", pCodecCtx->codec_id);

pCodec = avcodec_find_decoder(pCodecCtx->codec_id);

if(pCodec == NULL) {

fprintf(stderr, "can
not find decoder!n");

return -1;

}

/* Open
codec */

if(avcodec_open(pCodecCtx, pCodec)<0)

{

printf("cannot open software
codecn");

return -1; // Could not open
codec

}

printf("==========> Open software
codec successn");

pFrame = avcodec_alloc_frame();

if(pFrame == NULL)

{

fprintf(stderr, "avcodec_alloc_frame()
ERRORn");

return -1;

}

/* flag
whether we get a decoded yuv frame */

int frameFinished;

int packetno = 0;

AVPacket packet;

av_init_packet(&packet);

while(av_read_frame(pFormatCtx, &packet) >= 0) {

//printf("[main]avpkt->slice_count=%dn", packet.sliceNum);

/* Is this
a packet from the video stream? */

if(packet.stream_index == videoStream) {

packetno++;

#ifdef ENABLE_PRINT_FRAME_BYTES

if ( 1 ) {

int i;

int size = packet.size < PRINT_BYTES ? packet.size : PRINT_BYTES;

unsigned char *data = packet.data;

printf("===>[%5d]
[", packet.size);

for (i = 0; i < size; i++)

printf("%02x ", data[i]);

printf("]n");

}

#endif

#ifdef ENABLE_DEMUX_SAVE

fwrite(packet.data, 1, packet.size, frvdemux);

#endif

//printf("[the
%d packet]packet.size = %dn", packetno++, packet.size);

while (packet.size > 0) {

decLen = avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

//printf("[video_decode_example]after
avcodec_decode_video2,decoded=%dn",decLen);

if (decLen < 0) {

 
4000
; fprintf(stderr, "[video_decode_example]Error
while decoding frame %dn", frame);

//exit(1);

/* FIXME if decode
one frame err, ignore this
frame */

decLen = packet.size;

}

if (frameFinished) {

printf("got
a yuv framen");

//printf(stderr, "[video_decode_example]saving
frame %3dn", frame);

/* the
picture is allocated by the decoder. no
need to free it */

if (frame == 0) {

printf("[video_decode_example]picture->linesize[0]=%d,
c->width=%d,c->height=%dn",

pFrame->linesize[0], pCodecCtx->width, pCodecCtx->height);

printf("===>YUV
format = %dn", pFrame->format);

}

#ifdef ENABLE_YUV_SAVE

/* save
yuv pic */

if (frame < FRAME_NUM) {

switch (pFrame->format) {

case 0 : /* YUV420P */

yuv420p_save(pFrame, pCodecCtx);

break;

case 2 : /* RGB24 */

rgb24_save(pFrame, pCodecCtx);

break;

case 13 : /* YUVJ422P */

yuv422p_save(pFrame, pCodecCtx);

break;

case 14 : /* YUVJ444P */

yuv444p_save(pFrame, pCodecCtx);

break;

default :

fprintf(stderr, "unsupport
YUV format for savingn");

break;

}

fprintf(stderr, "===>save
pic successn");

}

#endif

/* frame
index grow */

frame++;

}

//printf("===========>
%dn", decLen);

/* left data in pkt , go on decoding */

packet.data += decLen;

packet.size -= decLen;

}

if (frame == FRAME_NUM) {

printf("==========>
decoded [%d pkt frames] ---> save [%d YUV frames], enough to stop!n", packetno, FRAME_NUM);

break;

}

}

/* FIXME
no need free in this file */

//printf("free
packet that was allocated by av_read_framen");

// Free
the packet that was allocated by av_read_frame

//av_free_packet(&packet);

}

printf("decoding job down!
begin to freen");

/* Free
the YUV frame */

av_free(pFrame);

/* Close
the codec */

avcodec_close(pCodecCtx);

/* Close
the video file */

av_close_input_file(pFormatCtx);

fclose(pfout);

printf("==========> END-OKn");

return 0;

}

最后是Makefile文件

点击(此处)折叠或打开

# use pkg-config for getting
CFLAGS abd LDFLAGS

FFMPEG_LIBS=libavdevice libavformat
libavfilter libavcodec libswscale libavutil

CFLAGS+=$(shell
pkg-config --cflags
$(FFMPEG_LIBS))

LDFLAGS+=$(shell
pkg-config --libs
$(FFMPEG_LIBS))

EXAMPLES=pic_dec

OBJS=$(addsuffix .o,$(EXAMPLES))

%: %.o

$(CC) $< $(LDFLAGS) -o
$@

%.o: %.c

$(CC) $< $(CFLAGS) -c -o
$@

.phony: all
clean

all: $(OBJS) $(EXAMPLES)

clean:

rm -rf $(EXAMPLES) $(OBJS)

注意如果是自己编译的ffmpeg-1.0等版本，安装到例如/usr/local/目录的话，需要在环境变量中设置

PKG_CONFIG_PATH和LD_LIBRARY_PATH，指定到/usr/local/lib/pkgconfig和/usr/local/lib/目录（如果以后要利用你的PC来交叉编译如VLC等开源代码，最好将这两个变量注释掉，因为交叉编译时的configure脚本会根据

这个配置错误的检查到PC也就是X86结构的lib，这个显然是不对的，会让VLC模块错误的认为你的机子上有了一些第三方的库，但VLC并不知道这是X86结构的）