VHS/Hi8 Digital Conversion: 25fps or 50fps (PAL)?

If the 25 fps is really interlaced (and you are able to those ugly interlacing lines with the correct display settings), you could "bob" deinterlace it as 50 fps so every field makes a whole temporally unique frame and then it might have slightly smoother motion. But if that 25 fps is in effect progressive, that is not possible. For example footage shot with a shutter speed slower than 1/50s is in effect progressive. Or if the capture workflow has already deinterlaced the footage (like the current QuickTime Player does no matter what -- the old QuickTime Player 7 could import interlaced footage).

Most VHS and Hi8 camcorder footage is going to be interlaced. Each field alone is a complete image of a unique moment in time, but at half resolution. Combining two fields correctly can improve detail while still maintaining the clear smooth motion of video. The high frame rate is one of the few good quality aspects of such video, so you don't want to lose it! 50 hz especially makes pans and bouncy camera work easier on the eye.

Unfortunately there is a lot of gear and software out there that was designed by people who don't understand interlace correctly. If objects move from one field to the next, combining the fields to display at once can be complicated. (On an old interlaced TV, your eye and brain would do the combining.) Look for Motion compensation deinterlacing.

To test if you are getting the best image, take the resulting files and go through them with frame advance, on a scene with lots of movement. Each time you press the button, the image should change. And you should not see mouse tooth distortion. The wikipedia article has good pics of that.

I've also encountered some "dumb" analog to HDMI converters that assume that all video is 16x9. There was nothing I could do about that, and I had to return it. Go figure.

Definitely go with 50fps or you will lose not only half of the spatial resolution, but half of the temporal resolution as well. When played back it should give a decent approximation of the interlacing you'd normally see. When you pause on a singe frame it'll look like hot garbage but that's OK.

Preserve both fields and double the frame rate to 50fps i.e. bob deinterlace 4:3 PAL .dv in FCP:

File > New... > Project > Custom > Resolution: 768x576, Rate: 50p, Color Space: Standard - Rec. 601 (PAL). Window > Show in Workspace > Inspector [cmd-4] > "i" [at upper right] > Basic to Settings [at lower right] > Field Dominance Override [at upper right] > Lower First/Off (Deinterlace OFF/ON does not seem to make any difference here). File > Share > HEVC - High Efficiency Video..., Settings > Format: Computer/Apple Devices, Video Codec: HEVC 10/8-bit [768x576 | 50fps].

But I usually do that in ffmpeg (slower but with slightly better quality than the defaults below with '-crf 18 -preset slow'):

ffmpeg -i input.dv -vf bwdif=1,scale=788:576,crop=768:576:10:0,setsar=sar=1/1,setparams=range=limited:color_primaries=bt470bg:color_trc=bt709:colorspace=smpte170m -c:v libx265 -crf 28 -preset medium -pix_fmt yuv420p10le -profile:v main10 -timecode 00:00:00:00 -tag:v hvc1 -c:a aac_at -b:a 128k PAL_dv_libx265_to_10bit_limited_5-1-6.mp4

Ian R. Brown wrote:

The tapes I am capturing are Video8 (lower quality than Hi8) so less than 480x360

I am not very familiar with Video8 but AFAIK PAL Video8, VHS, and Hi8 can all be captured at 702x576 rectangular pixels (and scaled to 788x576 and cropped to 768x576 square pixels). If the vertical resolution is less than 576, the interlacing is lost or might be even corrupted.

AFAIK PAL Video8, VHS, and Hi8 can all be captured at 702x576 rectangular pixels (and scaled to 788x576 and cropped to 768x576 square pixels). If the vertical resolution is less than 576, the interlacing is lost or might be even corrupted.

Minor correction: 702x576 is the usually sampled active PAL rectangular pixel picture frame that should be scaled to 768x576 square pixels. Likewise the padded 720x576 4:3 PAL DV should be cropped to 702x576 and scaled to 768x576 (or scaled to 788x576 and cropped to 768x576).