OpenCV encoding to H264 - c++

Question

I want to encode images to H264 video in OpenCV.
As part of my software for image tracking, I'm using VideoWriter in OpenCV 3.4 (64-bit) with Visual Studio 2017 C++. I use ffmpeg for manual encoding, and as it comes with OpenCV I assume this is the best option. My version of OpenCV indicates it has been compiled with ffmpeg, and I can verify it loads the opencv_ffmpeg340_64.dll.
Decoding H264 (AVC1) is absolutely fine, including when specifically using the ffmpeg API. But encoding anything other than MJPG or raw images doesn't work:
VideoWriter.Open() mostly returns false, for some cases it only writes an empty or small header but won't write frames. I've tried not only the ffmpeg API, but also any available API. Redirecting console/debug output to intermediate window in VC doesn't give any messages from OpenCV or ffmpeg.
There are numerous posts on previous versions of OpenCV using FFmpeg, including (Cisco) OpenH264 library and difficulties using this. I've tried many options, installing codecs pack including H264, ffmpeg static version, Cisco openH264 library, setting paths etc and even tried the low level ffmpeg library functions such as cvCreateVideoWriter exposed in OpenCV, and using different video containers (AVI, MPG, MP4) as well as fourcc strings.
I can't believe in 2018 the great OpenCV with FFmpeg support is unable to encode anything but arcane MJPG or raw images. If it uses FFmpeg surely a significant set of functionality should be available?
Though I think this should work, my next best option would be using a separate ffmpeg library, which would ironically add another ffmpeg.dll to my solution I imagine. Any suggestion appreciated!
Code fragment (using any video encoding API):
VideoWriter writer;
int codec = VideoWriter::fourcc('X', '2', '6', '4');
writer.open("test.avi", codec, 30, colorImage.size(), true);
writer.write(colorImage);
writer.release();

Answer 1

To answer my own question - thank you for the previous suggestions though - I've managed to create and write frames to H264 video now, without any recompiling needed. This is what I've used:
Using OpenCV version 3.4.1
In the same folder as the exe: opencv_ffmpeg341_64.dll (provided with OpenCV)
In the same folder: openh264-1.7.0-win64.dll (available from: https://github.com/cisco/openh264/releases)
Use OpenCV VideoWriter class, omitting a specific encoding API
Container: MP4
Codec fourcc string: "H264"
I formatted my machine (Windows 10 64bit) so I can't exclude any issues with potential codec-clashing - also I have not fully tested for other combinations. As this appears to be such a common problem (with many misconceptions) I hope this is useful.