[Libav-user] Help to convert MP4 to JPEG using libav* dlls downloaded from FFMPEG 3.3.2 for windows

venkatesh iyengar venkatesh_mk at yahoo.com
Mon Jul 31 02:56:31 EEST 2017

Hello,  From one week I am trying to convert MP4 to JPEG going thru different forums for examples, so far no success. Can you please share the link where you have seen it working successfully or you had it working on your projects using the libav shipped with FFMPEG 3.3.2 for windows shared/dev distribution. I am stuck right now and thumbnail extraction is important for of our project. I also tried the example that was part of the package, it generates pgm files, but I cannot convert it to any other viewable image formats. Please help.
/* * Copyright (c) 2001 Fabrice Bellard * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */
/** * @file * video decoding with libavcodec API example * * @example decode_video.c */
#include <stdio.h>#include <stdlib.h>#include <string.h>
#include <libavcodec/avcodec.h>
#define INBUF_SIZE 4096
static void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize,                     char *filename){    FILE *f;    int i;
    f = fopen(filename,"w");    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);}
static int decode_write_frame(const char *outfilename, AVCodecContext *avctx,                              AVFrame *frame, int *frame_count, AVPacket *pkt, int last){    int len, got_frame;    char buf[1024];
    len = avcodec_decode_video2(avctx, frame, &got_frame, pkt);    if (len < 0) {        fprintf(stderr, "Error while decoding frame %d\n", *frame_count);        return len;    }    if (got_frame) {        printf("Saving %sframe %3d\n", last ? "last " : "", *frame_count);        fflush(stdout);
        /* the picture is allocated by the decoder, no need to free it */        snprintf(buf, sizeof(buf), "%s-%d", outfilename, *frame_count);        pgm_save(frame->data[0], frame->linesize[0],                 frame->width, frame->height, buf);        (*frame_count)++;    }    if (pkt->data) {        pkt->size -= len;        pkt->data += len;    }    return 0;}
int main(int argc, char **argv){    const char *filename, *outfilename;    const AVCodec *codec;    AVCodecContext *c= NULL;    int frame_count;    FILE *f;    AVFrame *frame;    uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];    AVPacket avpkt;
    if (argc <= 2) {        fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);        exit(0);    }    filename    = argv[1];    outfilename = argv[2];
    /* set end of buffer to 0 (this ensures that no overreading happens for damaged MPEG streams) */    memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
    /* find the MPEG-1 video decoder */    codec = avcodec_find_decoder(AV_CODEC_ID_MPEG1VIDEO);    if (!codec) {        fprintf(stderr, "Codec not found\n");        exit(1);    }
    c = avcodec_alloc_context3(codec);    if (!c) {        fprintf(stderr, "Could not allocate video codec context\n");        exit(1);    }
    if (codec->capabilities & AV_CODEC_CAP_TRUNCATED)        c->flags |= AV_CODEC_FLAG_TRUNCATED; // we do not send complete frames
    /* For some codecs, such as msmpeg4 and mpeg4, width and height       MUST be initialized there because this information is not       available in the bitstream. */
    /* open it */    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);    }
    frame_count = 0;    for (;;) {        avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);        if (avpkt.size == 0)            break;
        /* NOTE1: some codecs are stream based (mpegvideo, mpegaudio)           and this is the only method to use them because you cannot           know the compressed data size before analysing it.
           BUT some other codecs (msmpeg4, mpeg4) are inherently frame           based, so you must call them with all the data for one           frame exactly. You must also initialize 'width' and           'height' before initializing them. */
        /* NOTE2: some codecs allow the raw parameters (frame size,           sample rate) to be changed at any frame. We handle this, so           you should also take care of it */
        /* here, we use a stream based decoder (mpeg1video), so we           feed decoder and see if it could decode a frame */        avpkt.data = inbuf;        while (avpkt.size > 0)            if (decode_write_frame(outfilename, c, frame, &frame_count, &avpkt, 0) < 0)                exit(1);    }
    /* Some codecs, such as MPEG, transmit the I- and P-frame with a       latency of one frame. You must do the following to have a       chance to get the last frame of the video. */    avpkt.data = NULL;    avpkt.size = 0;    decode_write_frame(outfilename, c, frame, &frame_count, &avpkt, 1);
    avcodec_free_context(&c);    av_frame_free(&frame);
    return 0;}

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