Saving frames as images using FFmpeg - c++

Question

There are some tutorials on the internet about it, most of them is using deprecated functions and unfortunately the API use to broke and it makes a mess and I'm really confused.
I'm following tutorials, learning with the documentation and seeing the examples of the current version (even that way some examples does not work).
What I'm trying to do is to save frames in .png, following the examples and reading I did this, but I'm confused about the conversion the frame to RBG and saving it:
#include <iostream>
extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/avutil.h>
}
int main(int argc, char ** argv)
{
if (argc < 2)
{
av_log(0, AV_LOG_FATAL, "Usage: %s <input>", argv[0]);
return -1;
}
const char * filename = argv[1];
// register all codecs and formats
av_register_all();
// open input file, and allocate format context
AVFormatContext *avFormatContext = avformat_alloc_context();
if (avformat_open_input(&avFormatContext, filename, 0, 0) < 0)
{
av_log(0, AV_LOG_FATAL, "Could not open source file %s", filename);
return -1;
}
// retrieve stream information
if (avformat_find_stream_info(avFormatContext, 0) < 0)
{
av_log(0, AV_LOG_FATAL, "Could not find stream information");
return -1;
}
// dump information about file onto standard error
av_dump_format(avFormatContext, 0, filename, 0);
// find the "best" video stream in the file.
int result = av_find_best_stream(avFormatContext, AVMEDIA_TYPE_VIDEO, -1, -1, 0, 0);
if (result < 0)
{
av_log(0, AV_LOG_FATAL, "Could not find %s stream in input file '%s'", av_get_media_type_string(AVMEDIA_TYPE_VIDEO), filename);
return -1;
}
int stream = result;
AVStream *avStream = avFormatContext->streams[stream];
AVCodecContext *avCodecContext = avStream->codec;
// find decoder for the stream
AVCodec *avCodec = avcodec_find_decoder(avCodecContext->codec_id);
if (! avCodec)
{
av_log(0, AV_LOG_FATAL, "Failed to find %s codec", av_get_media_type_string(AVMEDIA_TYPE_VIDEO));
return -1;
}
// init the decoders, with reference counting
AVDictionary *avDictionary = 0;
av_dict_set(&avDictionary, "refcounted_frames", "1", 0);
if (result = avcodec_open2(avCodecContext, avCodec, &avDictionary) < 0)
{
av_log(0, AV_LOG_FATAL, "Failed to open %s codec", av_get_media_type_string(AVMEDIA_TYPE_VIDEO));
return -1;
}
AVFrame *avFrame = av_frame_alloc();
if (! avFrame)
{
av_log(0, AV_LOG_FATAL, "Could not allocate frame");
return -1;
}
// initialize packet, set data to null, let the demuxer fill it
AVPacket avPacket;
av_init_packet(&avPacket);
avPacket.data = 0;
avPacket.size = 0;
while (av_read_frame(avFormatContext, &avPacket) >= 0)
{
if (avPacket.stream_index == stream)
{
int success = avcodec_decode_video2(avCodecContext, avFrame, &success, &avPacket);
if (success <= 0)
{
av_log(0, AV_LOG_FATAL, "Error decoding video frame");
return -1;
}
// ... saving...
}
}
avcodec_close(avCodecContext);
avformat_close_input(&avFormatContext);
av_frame_free(&avFrame);
return 0;
}