libavcodec encoding does not work

[AssemblerX86]

Summary of the bug:
Encoder at stream 0 (Mostly) does not get opened.
How to reproduce:

Try compiling "transcoding.c" example and trying "transcode vid.mp4 vid2.mp4"

Other than transcoding.c example, I have tried writing my code many times and not once it worked to encode a video (Tried different codecs for stream #0, but mainly h264), I get the error: "Tag avc1/<hex number here> incompatible with output codec id '28'" and then avformat_write_header returns error: "Invalid data found when processing input" and the program crashes when writing packets.

Here is the code:

#include "libavformat/avformat.h"
#include "libavcodec/avcodec.h"
#include "libavutil/avutil.h"
#include "libavutil/rational.h"
 
#include <stdio.h>
 
int main()
{
 
    av_register_all();
 
    //av_log_set_level(-8);
 
 
    AVFormatContext *ps = avformat_alloc_context();
 
    AVFormatContext *ps2 = avformat_alloc_context();
    AVOutputFormat *oF = av_guess_format("mp4", NULL, "video/mp4");
 
 
    if(avformat_open_input(&ps, "vid.mp4", NULL, NULL) != 0)
    {
        printf("Failed to open input file.\n");
        return -1;
    }
 
    avformat_alloc_output_context2(&ps2, ps->oformat, NULL, "vid2.mp4");
 
    avio_open(&ps2->pb, "vid2.mp4", AVIO_FLAG_WRITE);
 
    avformat_find_stream_info(ps, NULL);
 
   // AVStream *iStream;
    //AVStream *oStream;
 
    AVCodecContext *pC = avcodec_alloc_context3(NULL), *p2C = avcodec_alloc_context3(NULL);
    //AVCodec *encoder;
 
    AVStream *oStream = NULL;
    AVStream *iStream = NULL;
 
    AVCodec *encoder = NULL;
 
    for(unsigned int i = 0; i < ps->nb_streams; i++)
    {
        printf("%d\n", i);
        oStream = avformat_new_stream(ps2, NULL);
        iStream = ps->streams[i];
 
        avcodec_parameters_copy(oStream->codecpar, iStream->codecpar);
        //pC = iStream->codec;
        //p2C = oStream->codec;
 
 
        if(pC->codec_type == AVMEDIA_TYPE_VIDEO || pC->codec_type == AVMEDIA_TYPE_AUDIO)
        {
            //p2C = avcodec_alloc_context3(pC->codec);
            encoder = avcodec_find_encoder(pC->codec_id);
 
 
 
            /*oStream->time_base = iStream->time_base;
            p2C->pix_fmt = AV_PIX_FMT_YUV420P;
            p2C->flags = CODEC_FLAG_GLOBAL_HEADER;
            p2C->width = iStream->codec->width;
            p2C->height = iStream->codec->height;
            p2C->time_base = (AVRational){1, iStream->codec->framerate.num};
            p2C->gop_size = iStream->codec->framerate.num;
            p2C->bit_rate = iStream->codec->bit_rate;
            p2C->codec_tag = pC->codec_tag;
            //oStream->pts = iStream->pts;*/
 
            AVCodecParameters *par = avcodec_parameters_alloc();
            avcodec_parameters_from_context(par, pC);
            avcodec_parameters_to_context(p2C, par);
 
            avcodec_open2(p2C, encoder, NULL);
            avcodec_open2(pC, avcodec_find_decoder(pC->codec_id), NULL);
 
            //p2C-> = pC->pts;
        }
    }
    printf("done\n");
 
    int ret = avformat_write_header(ps2, NULL);
    char err[200];
    av_make_error_string(err, 200, ret);
    printf("Write header %d: %s\n", ret, err);
 
 
 
    AVFrame *rawFrame = av_frame_alloc();
 
    AVPacket *pkts = av_packet_alloc();
    //av_init_packet(pkts);
    AVPacket *pktr = av_packet_alloc();
    //av_init_packet(pktr);
 
    while(av_read_frame(ps, pkts) == 0)
    {
        //decoding
        if(avcodec_send_packet(pC, pkts) == 0)
        {
            if(avcodec_receive_frame(pC, rawFrame) == 0)
            {
            //encoding
                if(avcodec_send_frame(p2C, rawFrame) == 0)
                {
                    if(avcodec_receive_packet(p2C, pktr) == 0)
                    {
                        printf("Succ dec/enc\n");
                        if(av_interleaved_write_frame(ps2, pktr) != 0)
                        {
                            printf("Failed to write packet\n");
                            break;
                        }
                        printf("packet written\n");
                    }
                }
            }
        }
    }
    av_write_trailer(ps2);
    printf("Fine\n");
}

However, on transcoding.c, I get the error: "Cannot open video encoder for stream #0 \n Error occurred: Generic error in an external library"

Tried MSVC 2013 x32 and MinGW32.

[Carl Eugen Hoyos]

p2C->codec_tag = pC->codec_tag

As said elsewhere, this is not generally correct and will fail for mov -> mp4.