[Blake Sloan]

Doh. Yes. It may be possible (trying as I write this) to find the “sweet spot” duration parameter by iteratively encoding, reading the output duration with ffprobe and reducing the requested duration by some small number (trying with 1/100) until the output duration is less than the input, then using the previous iteration’s encoding. It is no longer fun. 🙂

[Blake Sloan]

Here’s a solution to the trailing white flash that seems to work for me when converting DnXHD to x264:

ffprobe

The result will have a line like:
> Duration:00:00:08.75 …

When encoding x264 (or other format)
Subtract 0.04 from this time code when passing the -t arg to ffmpeg.

ffmpeg -i -ss 00:00:00.0 -t 00:00:08.71