"Idle" MP4 -> MP4 conversion - video duration limit?

[Mr.Madguy]

Latest VLC 3.0.11 Win64. Codecs - standard MP4 (h264, MPEG Audio).

When I record video from notebook's camera or from HLS stream - there seem to be no MP4 video duration limit. I can record several hours of video. 2 hours, 3 hours, 5 hours. Problem is - when I record video from web camera, coding happens at real time, so compression ratio seems to be poor, i.e. I get very large file. Like several gigabytes. I want to decrease this size without loss of quality. So I perform "idle" MP4 -> MP4 conversion. It helps a lot, i.e. file size decreases to several hundreds of megabytes. Problem is: when I convert small file, like 40-60 minutes - this method works. But when I convert big file, like 2 hours, despite of conversion completing successfully (whole file is converted according to timer), output file becomes truncated. Like 15 minutes instead of 2 hours. Why this happens? What limits duration of output file? This happens both when I set and don't set "Stop time" in extra conversion parameters.

[Mr.Madguy]

UPD Seems like a bug, because ffmpeg doesn't have this problem. It's also more compatible with WMP, because it doesn't cause this "first frame freezing" effect. But may be it's just different default quality settings.