Anyway, after MUCHO testing (3 days of nonstop hassle), here are some results. Can't be 100% affirmative of course but, on — 32-bit only — old Win. XP,
"x264 CLI version: core:133 r2334 a3ac64b" (dated 2013...)
recodes my "7-mn HuffYUV .avi test", to impeccable frames only / tested 4 times, to "make sure"...
while both "ADM", "FFmpeg CLI" & even "x264 VfW via VirtualDub or else" * garble several frames every time.
x264 --crf 24 --preset medium --profile high --level 3.2 -o RESULT-vid_no-sound.mp4 Test-7-mn-HuffYUV.avi
* "x264 VfW via VirtualDub" goofed much less frames, but at least one, out of my test vid.
About "ADM on Linux": I've read the above "32-bit warning" post (of course) but still wanted to give it a try. Guess I'll need a dedicated PC, but none at hand at the moment:
so I only tried to install ADM on an Xubuntu v°, running from a "live USB key"... NO WAY! "Get-deb" being down, I had to give up, after wasting some 24 hours; ADM (whatever v° I download) just REFUSES to install / I must say that I know NOTHING about Linux, though. What worked in ~2014 did not, anymore.
Now, assuming that tests results are actually reliable (?? wouldn't bet a peanut, until further testing, on long footage), the silent .mp4 result vid. needs to be (re)muxed with its or some .aac audio stream
— using something ELSE than "FFmpeg", e.g. "Yamb/MP4box". Tested OK: no bad frames either.
Why? Because I also tried to save the test vid. w/ADM set to Copy & Copy, AND w/FFmpeg set to no recode... to end up with bad frames AGAIN: even in that case!
"In other words", back to the years ~2010 ** but "well", that's all I could get working (flawlessly).
[ ** as I intend to wear off those XP PCs until, say... 2050. Coming next: "How to encode to HEVC (x265) using a 1990 Amstrad PC?", since nothing's impossible, w/the help of Avidemux forum. ]
— BTW —, contrary to "FFmpeg" & "w264 VfW", since "x264 CLI" ONLY, recodes with no problem, doesn't it mean that "FFmpeg" & "x264 VfW" are somewhat buggy? OK: I KNOW that nobody wants to hear about 32 bits stuff anymore... Have I read the above answers? Yes I HAVE.
But it's "kind of" disappointing; I'll have to modify quite a few of my help/instructions to those friends etc., who (stubbornly) stick to Win. XP. I more or less understand them, though, after messing w/Win. 10 since ~2015. What about Linux then? Well, that's an other story, + another forum too, after all...