Summary

At FFMPEG Sink, field order is inverted when encoding.
But since bug #130 bugfix, it is now impacting both h264/mp4 and ffv1/mkv. Only h264 was impacted before.

For convenience I provided an experimental patch that fixes parity issues both for PAL and NTSC contents, both standards verified ok for ffv1 and h264 codecs. At least, "it works for me"(TM).
deinterlace_ok.patch

Steps to reproduce

1. Quick project, PAL or NTSC
2. FFMPEG Sink, interlaced, ffv1 or h264
3. Play with vlc or mpv with deinterlace

Expected behavior

Field parity fine at playback

Actual behavior

Field parity inverted at playback (motion stuttering)

Environment

• OS: Ubuntu 24.04
• Build/commit: nix 4b9db25
• Component: orc core

Additional context

First reason of the patch is that laserdiscs seem always to be TFF, be they PAL or NTSC.
Second reason is unclear, but frame_->flags |= AV_FRAME_FLAG_INTERLACED; somewhat seems to further discard |= AV_FRAME_TOP/BOTTOM_FIELD_FIRST