C:
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <stdio.h>
// compatibility with newer API
#if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(55,28,1)
#define av_frame_alloc avcodec_alloc_frame
#define av_frame_free avcodec_free_frame
#endif
void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
FILE *pFile;
char szFilename[32];
int y;
// Open file
sprintf(szFilename, "frame%d.ppm", iFrame);
pFile=fopen(szFilename, "wb");
if(pFile==NULL)
return;
// Write header
fprintf(pFile, "P6\n%d %d\n255\n", width, height);
// Write pixel data
for(y=0; y<height; y++)
fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);
// Close file
fclose(pFile);
}
int main(int argc, char *argv[]) {
// Initalizing these to NULL prevents segfaults!
AVFormatContext *pFormatCtx = NULL;
int i, videoStream;
AVCodecContext *pCodecCtxOrig = NULL;
AVCodecContext *pCodecCtx = NULL;
AVCodec *pCodec = NULL;
AVFrame *pFrame = NULL;
AVFrame *pFrameRGB = NULL;
AVPacket packet;
int frameFinished;
int numBytes;
uint8_t *buffer = NULL;
struct SwsContext *sws_ctx = NULL;
if(argc < 2) {
printf("Please provide a movie file\n");
return -1;
}
// Register all formats and codecs
av_register_all();
// Open video file
if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL)!=0)
return -1; // Couldn't open file
// Retrieve stream information
if(avformat_find_stream_info(pFormatCtx, NULL)<0)
return -1; // Couldn't find stream information
// Dump information about file onto standard error
av_dump_format(pFormatCtx, 0, argv[1], 0);
// Find the first video stream
videoStream=-1;
for(i=0; i<pFormatCtx->nb_streams; i++)
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
videoStream=i;
break;
}
if(videoStream==-1)
return -1; // Didn't find a video stream
// Get a pointer to the codec context for the video stream
pCodecCtxOrig=pFormatCtx->streams[videoStream]->codec;
// Find the decoder for the video stream
pCodec=avcodec_find_decoder(pCodecCtxOrig->codec_id);
if(pCodec==NULL) {
fprintf(stderr, "Unsupported codec!\n");
return -1; // Codec not found
}
// Copy context
pCodecCtx = avcodec_alloc_context3(pCodec);
if(avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0) {
fprintf(stderr, "Couldn't copy codec context");
return -1; // Error copying codec context
}
// Open codec
if(avcodec_open2(pCodecCtx, pCodec, NULL)<0)
return -1; // Could not open codec
// Allocate video frame
pFrame=av_frame_alloc();
// Allocate an AVFrame structure
pFrameRGB=av_frame_alloc();
if(pFrameRGB==NULL)
return -1;
// Determine required buffer size and allocate buffer
numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
pCodecCtx->height);
buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
// Assign appropriate parts of buffer to image planes in pFrameRGB
// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
// of AVPicture
avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
pCodecCtx->width, pCodecCtx->height);
// initialize SWS context for software scaling
sws_ctx = sws_getContext(pCodecCtx->width,
pCodecCtx->height,
pCodecCtx->pix_fmt,
pCodecCtx->width,
pCodecCtx->height,
PIX_FMT_RGB24,
SWS_BILINEAR,
NULL,
NULL,
NULL
);
// Read frames and save first five frames to disk
i=0;
while(av_read_frame(pFormatCtx, &packet)>=0) {
// Is this a packet from the video stream?
if(packet.stream_index==videoStream) {
// Decode video frame
avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
// Did we get a video frame?
if(frameFinished) {
// Convert the image from its native format to RGB
sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
pFrame->linesize, 0, pCodecCtx->height,
pFrameRGB->data, pFrameRGB->linesize);
// Save the frame to disk
if(++i<=5)
SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height,
i);
}
}
// Free the packet that was allocated by av_read_frame
av_free_packet(&packet);
}
// Free the RGB image
av_free(buffer);
av_frame_free(&pFrameRGB);
// Free the YUV frame
av_frame_free(&pFrame);
// Close the codecs
avcodec_close(pCodecCtx);
avcodec_close(pCodecCtxOrig);
// Close the video file
avformat_close_input(&pFormatCtx);
return 0;
}
Come da titolo mi escono degli errori nella compilazione: rinomino il file in .c,
da linux: cc -I ... prova.c -o prova
warning: implicit declaration of function ‘avformat_open_input’ [-Wimplicit-function-declaration]
request for member ‘nb_streams’ in something not a structure or union
for(i=0; i<pFormatCtx->nb_streams; i++) .. ecc
gli errori sono questi:
prova.c: In function ‘main’:
prova.c:60:6: warning: implicit declaration of function ‘avformat_open_input’; did you mean ‘avformat_free_context’? [-Wimplicit-function-declaration]
if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL)!=0)
^~~~~~~~~~~~~~~~~~~
avformat_free_context
prova.c:64:6: warning: implicit declaration of function ‘avformat_find_stream_info’; did you mean ‘av_find_stream_info’? [-Wimplicit-function-declaration]
if(avformat_find_stream_info(pFormatCtx, NULL)<0)
^~~~~~~~~~~~~~~~~~~~~~~~~
av_find_stream_info
prova.c:96:6: warning: implicit declaration of function ‘avcodec_open2’; did you mean ‘avcodec_open’? [-Wimplicit-function-declaration]
if(avcodec_open2(pCodecCtx, pCodec, NULL)<0)
^~~~~~~~~~~~~
avcodec_open
prova.c:12:23: warning: implicit declaration of function ‘avcodec_free_frame’; did you mean ‘avcodec_parse_frame’? [-Wimplicit-function-declaration]
#define av_frame_free avcodec_free_frame
^~~~~~~~~~~~~~~~~~
prova.c:159:3: note: in expansion of macro ‘av_frame_free’
av_frame_free(&pFrameRGB);
^~~~~~~~~~~~~
prova.c:169:3: warning: implicit declaration of function ‘avformat_close_input’; did you mean ‘avformat_license’? [-Wimplicit-function-declaration]
avformat_close_input(&pFormatCtx);
^~~~~~~~~~~~~~~~~~~~
avformat_license
/usr/bin/ld: /tmp/ccvNkKXf.o: in function `main':
prova.c:(.text+0x142): undefined reference to `av_register_all'
/usr/bin/ld: prova.c:(.text+0x16b): undefined reference to `avformat_open_input'
/usr/bin/ld: prova.c:(.text+0x18f): undefined reference to `avformat_find_stream_info'
/usr/bin/ld: prova.c:(.text+0x1c1): undefined reference to `av_dump_format'
/usr/bin/ld: prova.c:(.text+0x246): undefined reference to `avcodec_find_decoder'
/usr/bin/ld: prova.c:(.text+0x287): undefined reference to `avcodec_alloc_context3'
/usr/bin/ld: prova.c:(.text+0x29e): undefined reference to `avcodec_copy_context'
/usr/bin/ld: prova.c:(.text+0x2e9): undefined reference to `avcodec_open2'
/usr/bin/ld: prova.c:(.text+0x2fc): undefined reference to `avcodec_alloc_frame'
/usr/bin/ld: prova.c:(.text+0x305): undefined reference to `avcodec_alloc_frame'
/usr/bin/ld: prova.c:(.text+0x336): undefined reference to `avpicture_get_size'
/usr/bin/ld: prova.c:(.text+0x343): undefined reference to `av_malloc'
/usr/bin/ld: prova.c:(.text+0x36f): undefined reference to `avpicture_fill'
/usr/bin/ld: prova.c:(.text+0x3aa): undefined reference to `sws_getContext'
/usr/bin/ld: prova.c:(.text+0x3eb): undefined reference to `avcodec_decode_video2'
/usr/bin/ld: prova.c:(.text+0x439): undefined reference to `sws_scale'
/usr/bin/ld: prova.c:(.text+0x473): undefined reference to `av_free_packet'
/usr/bin/ld: prova.c:(.text+0x489): undefined reference to `av_read_frame'
/usr/bin/ld: prova.c:(.text+0x49d): undefined reference to `av_free'
/usr/bin/ld: prova.c:(.text+0x4ae): undefined reference to `avcodec_free_frame'
/usr/bin/ld: prova.c:(.text+0x4bf): undefined reference to `avcodec_free_frame'
/usr/bin/ld: prova.c:(.text+0x4cb): undefined reference to `avcodec_close'
/usr/bin/ld: prova.c:(.text+0x4d7): undefined reference to `avcodec_close'
/usr/bin/ld: prova.c:(.text+0x4e8): undefined reference to `avformat_close_input'
collect2: error: ld returned 1 exit status
dovrei dichiarare le funzioni (per iniziare) ma non sono riuscito
grazie
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