On 16/03/2019 11:40, J. P. Gilliver (John) wrote:

Can a video file change resolution part way through?

Unfortunately, yes, and it's a f*ker to deal with if you want to keep a
program whose content is decent but it's been poorly put together, so as
to do that.

Firstly, videos recorded by some PVRs can do this *by design*, for
exanple some of the Panasonic DMR series. If you plan to copy
recordings from these machines to your PC for processing into DVDs or
conventional video formats such as mkv or mp4, you'd probably best
disable this setting - certainly for DVDs you *must* do so:

http://www.macfh.co.uk/JavaJive/Audi...C.html#setting

But too often it happens by cock-up of the broadcaster. I've recently
been going through my old Dreambox, Panasonic DMR, and VCR recordings
and have found a number of examples of this (most of them were actually
switches in aspect ratio rather than actual changes in resolution, but
the difficulties seem to be much the same in both cases). I can
remember for example ...

'Life In The Freezer - 1 Bountiful Sea' began in widescreen, but at 5:08
somebody realised the mistake and corrected it to its original 4:3.
Unfortunately, I couldn't find a way of correcting this seamlessly - I
had to split the file into two at that point, process the two parts
differently, then join them together again, with the result that there
is a glitch at the point of the join.

Several episodes of 'The Singing Detective' had widescreen leading
titles, before switching to 4:3 for the actual content. However this
was easier to deal with, because the two parts were separated by a
silent blank screen.

Then, of course, there are the ad-breaks in programmes or films shown on
commercial channels, but, although it can be tedious trying to find the
right point at which to edit, because sometimes the sound or picture
cross fades between the two, in the long run, because you don't want to
keep the ads, it's a matter of choice where to cut. Also, some
transport streams and formats allow finer editing control than others -
for example it can be very difficult to edit an mp4 as accurately as
desired to preserve just the part you want because inevitably the
available cut point are either too early or too late.