ffmpeg create RTP stream - c++

Question

I'm trying to encode and stream using ffmpeg (libavcodec/libavformat - MSVC x64 with Zeranoe builds)
Here is my code, largely adapted from the encoding example, error handling removed
#include "stdafx.h"
extern "C" {
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/channel_layout.h>
#include <libavutil/common.h>
#include <libavutil/imgutils.h>
#include <libavutil/mathematics.h>
#include <libavutil/samplefmt.h>
}
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "avcodec.lib")
int main() {
avcodec_register_all();
av_register_all();
avformat_network_init();
AVCodecID codec_id = AV_CODEC_ID_H264;
AVCodec *codec;
AVCodecContext *c = NULL;
int i, ret, x, y, got_output;
AVFrame *frame;
AVPacket pkt;
codec = avcodec_find_encoder(codec_id);
c = avcodec_alloc_context3(codec);
c->bit_rate = 400000;
c->width = 352;
c->height = 288;
c->time_base.num = 1;
c->time_base.den = 25;
c->gop_size = 25;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;
c->codec_type = AVMEDIA_TYPE_VIDEO;
c->flags = CODEC_FLAG_GLOBAL_HEADER;
if (codec_id == AV_CODEC_ID_H264) {
ret = av_opt_set(c->priv_data, "preset", "ultrafast", 0);
ret = av_opt_set(c->priv_data, "tune", "zerolatency", 0);
}
avcodec_open2(c, codec, NULL)
frame = av_frame_alloc();
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
c->pix_fmt, 32);
AVFormatContext* avfctx;
AVOutputFormat* fmt = av_guess_format("rtp", NULL, NULL);
ret = avformat_alloc_output_context2(&avfctx, fmt, fmt->name,
"rtp://127.0.0.1:49990");
printf("Writing to %s\n", avfctx->filename);
avio_open(&avfctx->pb, avfctx->filename, AVIO_FLAG_WRITE)
struct AVStream* stream = avformat_new_stream(avfctx, codec);
stream->codecpar->bit_rate = 400000;
stream->codecpar->width = 352;
stream->codecpar->height = 288;
stream->codecpar->codec_id = AV_CODEC_ID_H264;
stream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
stream->time_base.num = 1;
stream->time_base.den = 25;
avformat_write_header(avfctx, NULL);
char buf[200000];
AVFormatContext *ac[] = { avfctx };
av_sdp_create(ac, 1, buf, 20000);
printf("sdp:\n%s\n", buf);
FILE* fsdp;
fopen_s(&fsdp, "test.sdp", "w");
fprintf(fsdp, "%s", buf);
fclose(fsdp);
system("PAUSE");
system("start "" \"C:\\Program Files (x86)\\VideoLAN\\VLC\\vlc.exe\" test.sdp");
int j = 0;
for (i = 0; i < 10000; i++) {
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
fflush(stdout);
/* prepare a dummy image */
/* Y */
for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width; x++) {
frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
}
}
/* Cb and Cr */
for (y = 0; y < c->height / 2; y++) {
for (x = 0; x < c->width / 2; x++) {
frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
}
}
frame->pts = i;
/* encode the image */
ret = avcodec_send_frame(c, frame);
ret = avcodec_receive_packet(c, &pkt);
if (ret == AVERROR_EOF) {
got_output = false;
printf("Stream EOF\n");
} else if(ret == AVERROR(EAGAIN)) {
got_output = false;
printf("Stream EAGAIN\n");
} else {
got_output = true;
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", j++, pkt.size);
av_interleaved_write_frame(avfctx, &pkt);
av_packet_unref(&pkt);
}
Sleep(40);
}
// end
ret = avcodec_send_frame(c, NULL);
/* get the delayed frames */
for (; ; i++) {
fflush(stdout);
ret = avcodec_receive_packet(c, &pkt);
if (ret == AVERROR_EOF) {
printf("Stream EOF\n");
break;
} else if (ret == AVERROR(EAGAIN)) {
printf("Stream EAGAIN\n");
got_output = false;
} else {
got_output = true;
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", j++, pkt.size);
av_interleaved_write_frame(avfctx, &pkt);
av_packet_unref(&pkt);
}
}
avcodec_close(c);
av_free(c);
av_freep(&frame->data[0]);
av_frame_free(&frame);
printf("\n");
system("pause");
return 0;
}
However VLC (opened with the generated SDP file) isn't able to play the stream. Messages has this
core error: ES_OUT_RESET_PCR called
followed by repeated
packetizer_h264 warning: waiting for SPS/PPS
core debug: Buffering <some percent>%
What am I doing wrong?

Answer 1

After a few hours of digging in the ffmpeg source, I found the solution:
Don't use the CODEC_FLAG_GLOBAL_HEADER flag
Use avformat_write_header before each av_interleaved_write_frame
Now VLC plays the stream correctly