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can videos change resolution/aspect ratio mid-stream?



 
 
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  #1  
Old March 16th 19, 12:40 PM posted to microsoft.public.windowsxp.general,alt.windows7.general
J. P. Gilliver (John)[_4_]
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Default can videos change resolution/aspect ratio mid-stream?

Reading a post (from Paul) in the "What software is used to edit MP4
videos?" thread (in the XP 'group), reminded me to wonder something I've
been wondering for some time:

Can a video file change resolution part way through? I'm not talking
about where it is all at the highest resolution and parts are
"letterboxed", "pillarboxed", or "postage-stamped", i. e. don't fill the
frame but the rest is filled with black (or other colour, or even
patterned!), but a genuine change of resolution. Or, I suppose, other
parameters - frame rate, colour depth (or colour/monochrome), number of
soundtracks, or probably other things I haven't thought of.

If it can, do any of the editors in common use handle such a transition?

I was, among other things, wondering what happens if you splice together
two segments (which I think most of the editors can do) that have
different resolutions/aspect ratios.

(If the answer is yes they can, I expect it's only some video formats?)
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  #2  
Old March 16th 19, 01:22 PM posted to microsoft.public.windowsxp.general,alt.windows7.general
Java Jive
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Default can videos change resolution/aspect ratio mid-stream?

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.
  #3  
Old March 16th 19, 02:21 PM posted to microsoft.public.windowsxp.general,alt.windows7.general
Paul[_32_]
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Posts: 8,732
Default can videos change resolution/aspect ratio mid-stream?

J. P. Gilliver (John) wrote:
Reading a post (from Paul) in the "What software is used to edit MP4
videos?" thread (in the XP 'group), reminded me to wonder something I've
been wondering for some time:

Can a video file change resolution part way through? I'm not talking
about where it is all at the highest resolution and parts are
"letterboxed", "pillarboxed", or "postage-stamped", i. e. don't fill the
frame but the rest is filled with black (or other colour, or even
patterned!), but a genuine change of resolution. Or, I suppose, other
parameters - frame rate, colour depth (or colour/monochrome), number of
soundtracks, or probably other things I haven't thought of.

If it can, do any of the editors in common use handle such a transition?

I was, among other things, wondering what happens if you splice together
two segments (which I think most of the editors can do) that have
different resolutions/aspect ratios.

(If the answer is yes they can, I expect it's only some video formats?)


The quickest way I could answer this, is to look at the
format specification for a "container". Like this AVI spec:

https://web.archive.org/web/20171211...8.com/avi.html

There's only one header per file, that I can see there.
And that is where the width and height are.

There are multiple container formats (.mov, .mp4, .mkv, .avi), and
they don't necessarily all have to work the same way. But it helps...

You would have to go through the syntax spec for each
container design, and see if multiple header chunks
are allowed.

And remember that your video has to play both forwards
and backwards (for jog and shuttle). The first segment
could end in mid-GOP, followed by a second segment
of a different WxH. Now, play that mess backwards.
Can you imagine the mayhem this would cause ? Or,
imagine the user selected "full screen" for video
playback, then the movie res changes after the
first scene. What happens ? Eww.

I think it's easier to bring all the videos to
a common resolution before rendering them. The video
render resolution does not have to be equal to the
resolution of the frames. I can be editing a 1920x1080
video, and render out to 1280x720 to save on bitrate
and file size. So all the segments originally
recorded at some other values, could end up being
converted to 1280x720 when my final video out is made.
And the video just looks a bit more fuzzy, the smaller
the output render resolution happens to be. If I
render to 160x120, I save a ton of file size, and
the video looks terrible :-) And when I use my "player"
later, it will automatically up-scale to mostly
fill my screen. Rather than obediently play at 160x120
in a tiny little window.

Paul
  #4  
Old March 16th 19, 02:58 PM posted to microsoft.public.windowsxp.general,alt.windows7.general
J. P. Gilliver (John)[_4_]
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Posts: 2,531
Default can videos change resolution/aspect ratio mid-stream?

In message , Java Jive
writes:
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


Ah, I hadn't thought of videos recorded off-air, where the broadcasters
change what they're putting out, as they do at least between prog.s and
often do for the ad. breaks.
[rest snipped - interesting, thanks.]
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)[email protected]+H+Sh0!:`)DNAf

"You _are_ Zaphod Beeblebrox? _The_ Zaphod Beeblebrox?"
"No, just _a_ Zaphod Beeblebrox. I come in six-packs." (from the link episode)
 




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