[Libav-user] decode_video example pgm files distorted?(v4.0.2Winbuild)
Strahinja Radman
dr.strashni at gmail.com
Tue Sep 4 22:06:16 EEST 2018
Hey Chris,
I am not sure how exactly you modified your code but this should be the look of the loop
while(av_read_frame(fmt_ctx, &packet) > 0)
{
decode(c, frame, pkt, outfilename);
}
Kind regards,
Strahinja
From: Chris Bennett
Sent: 04 September 2018 20:54
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter.
Subject: Re: [Libav-user] decode_video example pgm files distorted?(v4.0.2Winbuild)
Hm. Here is something strange.
When I try using while(av_read_frame(fmt_ctx, &packet) > 0), the method immediately passes, making nothing happen.
I turned on debug in my stream, and this is the output (not much makes sense/looks useful to me)
https://drive.google.com/file/d/1Twft75sGLGGsHN5tuwkcI1KQVsPM5lt4/view?usp=sharing
Let me know what you think. Thanks!
Chris Bennett
On Sat, Sep 1, 2018 at 12:48 AM, Strahinja Radman <dr.strashni at gmail.com> wrote:
Hey Chris,
Can you try using
while(av_read_frame(fmt_ctx, &packet) > 0)
instead of using
while(!feof(f))
and then just send a packet to your decode method instead of a raw frame?
From: Chris Bennett
Sent: 31 August 2018 22:57
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter.
Subject: Re: [Libav-user] decode_video example pgm files distorted? (v4.0.2Winbuild)
Hey Strahinja!
Thank you very much for taking the time to help me out.
the pgm snippet you sent looks the same as the decode video example I am seeing.
Here is the code that I am compiling and running if it helps, hopefully its not too long. ( I had to add an extern "C" wrapper since my goal is to build c++ tools with this, and also changed how the example finds the decoder).
/*
* 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>
extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat\avformat.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 void 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);
pgm_save(frame->data[0], frame->linesize[0],
frame->width, frame->height, buf);
}
}
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;
if (argc <= 2) {
fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
exit(0);
}
filename = argv[1];
outfilename = argv[2];
pkt = av_packet_alloc();
if (!pkt)
exit(1);
/* 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);
//---from test1.cpp
AVFormatContext *pFormatContext = avformat_alloc_context();
if (!pFormatContext) {
fprintf(stderr, "ERROR could not allocate memory for Format Context");
return -1;
}
if (avformat_open_input(&pFormatContext, argv[1], NULL, NULL) != 0) {
fprintf(stderr, "ERROR could not open the file");
return -1;
}
AVCodecParameters *pLocalCodecParameters = NULL;
pLocalCodecParameters = pFormatContext->streams[0]->codecpar;
//-----
/* find the video decoder */
//codec = avcodec_find_decoder(AV_CODEC_ID_MJPEG);
codec = avcodec_find_decoder(pLocalCodecParameters->codec_id);
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);
}
/* 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);
}
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, 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->size)
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;
}
Please let me know if you see anything incorrect with this.
Thanks!
Chris Bennett
Lead Animation Pipeline TD - Television
On Fri, Aug 31, 2018 at 10:48 AM, Strahinja Radman <dr.strashni at gmail.com> wrote:
Hi Chris,
To me that looks like you wrote some wrong data inside the picture and it looks skewed. Some indexes could be wrong.
void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize, const 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);
}
The above method should be called with pgm_save(frame->data[0], frame->linesize[0], frame->width, frame->height, “name.pgm”);
Kind regards,
Strahinja
From: Chris Bennett
Sent: 31 August 2018 19:41
To: libav-user at ffmpeg.org
Subject: [Libav-user] decode_video example pgm files distorted? (v4.0.2 Winbuild)
Hello All!
My apologies if this is a rookie question as I am just now learning the innards of ffmpeg, but I am reaching out hoping someone may have had the same issue as myself or has any advice.
I cloned 4.0.2 and compiled the libraries (MS VS 2013 x64) without issue.
I decided to try the examples as a learning opportunity, choosing decode_video. I ended up with this result: https://drive.google.com/file/d/1DPu1EaM7i5J3LFaaGmZNO4Hoi_QzVcKM/view?usp=sharing
At the top and bottom of the image there is is wavy distortion. I am not sure what is causing it.
The source file is a quicktime of a Motion JPEG video.
I had also compiled the exe as well and ran this command
ffmpeg.exe -ss 0.5 -i my_quicktime.mov -t 1 -s 480x300 -f image2 C:/frame-%03d.jpg
and those images turned out just fine (I am sure this probably runs some completely different underlying code but I just wanted to make sure what I compiled was capable of a successful result)
I figure I am doing something incorrectly but I do not know where else to look. If anyone has any advice on what to tinker with, I would greatly appreciate it.
Thanks,
Chris Bennett
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