x264 output video is blank when threading is enabled - c++

Question

I am using libx264 compiled from source. It was configured to get both .dll and .lib by this command
./configure --disable-cli --enable-shared --extra-ldflags=-Wl,--output-def=libx264.def`
I am using the libx264 API in my screen-sharing program with the preset - "veryfast", tune - "zerolatency", profile - "high" and also the following settings.
param.i_csp = X264_CSP_BGRA;
param.i_threads = 1;
param.i_width = width;
param.i_height = height;
param.i_fps_num = fps;
param.i_fps_den = 1;
param.rc.i_bitrate = bitrate;
param.rc.i_rc_method = X264_RC_ABR;
param.rc.b_filler = true;
param.rc.f_rf_constant = (float)0;
param.rc.i_vbv_max_bitrate = param.rc.i_bitrate;
param.rc.i_vbv_buffer_size = param.rc.i_bitrate;
param.b_repeat_headers = 0;
param.b_annexb = 1;
For these settings the program works fine. I specified it as single threaded by setting param.i_threads = 1.
If this is removed, x264 defaults to using multiple threads and sets param.i_threads as 1.5x of number of cores in the CPU automatically. This will give faster performance than running in single thread.
But when I remove the param.i_threads = 1 to make it multi-threaded, the generated output is fully grey. I cannot see any output when I view the live stream with VLC or some times I can view a weird output.
I am using this bitmap image as an example (https://imgur.com/a/l8LCd1l). Only this same image is being encoded multiple times. When it is saved into .h264 video, it is viewable clearly. But when the encoded payload is sent through rtmp, the live stream produces very bad and weird output (or sometimes no output). This is the weird output which im seeing most of the time for this image: https://imgur.com/a/VdyX1Zm
This is the full example code in which I am both streaming and writing video file of the same picture. This is using the srs librtmp library. There is no error but the stream has weird output.
In this code if you set add param.i_threads = 1; then only the output stream will be viewable. The problem is that it should be viewable in both single-threaded and multi-threaded encoding.
#include <iostream>
#include <stdio.h>
#include <sstream>
#include <x264.h>
#include "srs_librtmp.h"
#pragma comment(lib, "C:/Softwares/x264/libx264.lib")
using namespace std;
int check_ret(int ret);
int main()
{
int dts = 0;
x264_param_t param;
x264_t* h;
x264_nal_t* nals;
int i_nal;
int pts = 0;
int i_frame_size;
x264_picture_t picIn;
x264_picture_t picOut;
x264_param_default_preset(&param, "veryfast", "zerolatency");
//x264 settings
param.i_csp = X264_CSP_BGRA;
param.i_width = 1920;
param.i_height = 1080;
param.i_fps_num = 30;
param.i_fps_den = 1;
param.rc.i_bitrate = 2500;
param.rc.i_rc_method = X264_RC_ABR;
param.rc.b_filler = true;
param.rc.f_rf_constant = (float)0;
param.rc.i_vbv_max_bitrate = param.rc.i_bitrate;
param.rc.i_vbv_buffer_size = param.rc.i_bitrate;
param.b_repeat_headers = 0;
param.b_annexb = 1;
x264_param_apply_profile(&param, "high");
h = x264_encoder_open(&param);
//allocate picture
x264_picture_alloc(&picIn, param.i_csp, param.i_width, param.i_height);
//picture settings
picIn.img.i_plane = 1;
picIn.img.i_stride[0] = 4 * param.i_width;
picIn.i_type = X264_TYPE_AUTO;
int header_size = x264_encoder_headers(h, &nals, &i_nal);
FILE* fptr;
fopen_s(&fptr, "example1.h264", "wb");
// write sps and pps in the video file
fwrite(nals->p_payload, header_size, 1, fptr);
int size = 1920 * 1080 * 4;
char* bmp = new char[size];
FILE* bitptr;
errno_t err = fopen_s(&bitptr, "flower.bmp", "rb");
fseek(bitptr, 54, SEEK_SET);
fread(bmp, size, 1, bitptr);
fclose(bitptr);
srs_rtmp_t rtmp = srs_rtmp_create("127.0.0.1:1935/live/test");
if (srs_rtmp_handshake(rtmp) != 0)
{
std::cout << "Simple handshake failed.";
return -1;
}
std::cout << "Handshake completed successfully.\n";
if (srs_rtmp_connect_app(rtmp) != 0) {
std::cout << "Connecting to host failed.";
return -1;
}
std::cout << "Connected to host successfully.\n";
if (srs_rtmp_publish_stream(rtmp) != 0) {
std::cout << "Publish signal failed.";
}
std::cout << "Publish signal success\n";
// write sps and pps in the live stream
int ret = srs_h264_write_raw_frames(rtmp, reinterpret_cast<char*>(nals->p_payload), header_size, 0, 0);
ret = check_ret(ret);
if (!ret)
return -1;
std::cout << "SPS and PPS sent.\n";
// main loop
std::cout << "Now streaming and encoding\n";
int i = 1800;
while (i--)
{
picIn.img.plane[0] = reinterpret_cast<uint8_t*>(bmp);
picIn.i_pts = pts++;
i_frame_size = x264_encoder_encode(h, &nals, &i_nal, &picIn, &picOut);
if (i_frame_size)
{
for (int j = 0; j < i_nal; j++)
{
x264_nal_t* nal = nals + j;
// write data in the video file
fwrite(nal->p_payload, nal->i_payload, 1, fptr);
// write data in the live stream
ret = srs_h264_write_raw_frames(rtmp, reinterpret_cast<char*>(nal->p_payload), nal->i_payload, dts, dts);
ret = check_ret(ret);
if (!ret)
{
return -1;
}
}
}
else
{
std::cout << "i_frame_size = 0 (encoder failed)\n";
}
dts += 33;
}
while (x264_encoder_delayed_frames(h))
{
i_frame_size = x264_encoder_encode(h, &nals, &i_nal, NULL, &picOut);
if (i_frame_size)
{
fwrite(nals->p_payload, i_frame_size, 1, fptr);
}
}
std::cout << "\nAll done\n";
std::cout << "Output video is example1.h264 and it is viewable in VLC";
return 0;
}
int check_ret(int ret)
{
if (ret != 0) {
if (srs_h264_is_dvbsp_error(ret)) {
srs_human_trace("ignoring drop video error, code=%d", ret);
}
else if (srs_h264_is_duplicated_sps_error(ret)) {
srs_human_trace("ignoring duplicated sps, code=%d", ret);
}
else if (srs_h264_is_duplicated_pps_error(ret)) {
srs_human_trace("ignoring duplicated pps, code=%d", ret);
}
else {
srs_human_trace("sending h264 raw data failed. ret=%d", ret);
return 0;
}
}
return 1;
}
If you would like to download the original flower.bmp file, here is the link: https://gofile.io/d/w2kX56
This error can be reproduced in any other bmp file also.
Please tell me what is causing this problem when multi-threading is enabled. Am I setting wrong values? Is the code in which I am streaming the encoded data wrong?