Crash while opening a RTMP file using ffmpeg - ffmpeg

Question

I have written code to play video using ffmpeg.
The code works fine when i open AVI files but when i try to open a RTMP feed i get error.
in the utils.c file in the following function of the utils.c file
utils.c
int avcodec_parameters_to_context(AVCodecContext *codec,
const AVCodecParameters *par)
{
codec->codec_type = par->codec_type; // crash happens at this line.
}
**par was nullptr
this is my code
if (load_frame("rtmp://192.168.1.2/live/sumit", &file_width, &file_height, &myData)) {
std::cout << "file Loaded";
}
defination for load_frame function
AVFormatContext *av_format_ctx = avformat_alloc_context();
if (!av_format_ctx) {
std::cout << "could not create a format context\n";
return false;
}
if (avformat_open_input(&av_format_ctx, filename, NULL, NULL) < 0) {
std::cout << "Couldn't open video file\n";
return false;
}
AVCodecParameters* av_codec_params = nullptr;
AVCodec* av_codec = nullptr;
int video_stream_index = -1;
for (unsigned int i = 0; i < av_format_ctx->nb_streams; i++) {
auto stream = av_format_ctx->streams[i];
av_codec_params = av_format_ctx->streams[i]->codecpar;
av_codec = avcodec_find_decoder(av_codec_params->codec_id);
if (!av_codec) {
std::cout << "Couldn't find the codec\n";
continue;
}
if (av_codec_params->codec_type == AVMEDIA_TYPE_VIDEO)
{
video_stream_index = i;
std::cout << "Video stream found" << std::endl;
break;
}
if (video_stream_index < 0)
return false;
}
// set up codec context for the decoder
AVCodecContext* av_codec_ctx = avcodec_alloc_context3(av_codec);
if (!av_codec_ctx) {
std::cout << "Couldn't create AV context";
return false;
}
// this function invokes the error
if (avcodec_parameters_to_context(av_codec_ctx, av_codec_params) < 0) {
std::cout << "Couldn't initialize AVCodecContext";
return false;
}
////////////////// EDIT /////////////////////////////////
I am streaming a mpeg file and av_format_ctx->nb_streams return value of 0 , why is it not able to find any streams.
i can view the same file on vlc through streaming option in vlc.

Answer 1

Think of avformat_open_input like fopen. It will open a stream/file, but you still do not have an information on the stream/file contents, only a handle to do further operation with.
If you want to actually look at the data in the stream/file, you must first read the headers to determine what is inside. avformat_find_stream_info will accomplish that