OK you wise guys! How come, when I play a programme backwards on the
PVR, the subtitles aren't written backwards?

Seamus

On Sat 22/01/2022 21:02, williamwright wrote:
> OK you wise guys! How come, when I play a programme backwards on the
> PVR, the subtitles aren't written backwards?
>
> Seamus

You are only showing the movement in reverse, the picture isn't reversed
is it?

So why should the subtitles be backwards?

"Woody" <harrogate3@ntlworld.com> wrote in message
news:sshrpb$bs8$1@dont-email.me...
> On Sat 22/01/2022 21:02, williamwright wrote:
>> OK you wise guys! How come, when I play a programme backwards on the PVR,
>> the subtitles aren't written backwards?
>>
>> Seamus
>
> You are only showing the movement in reverse, the picture isn't reversed
> is it?
>
> So why should the subtitles be backwards?

If you load a VHS video tape upside down (by unreeling it and winding it the
opposite way on the spools) the picture is upside down, as well as being
very ragged because the sync pulses are in the wrong place. I had a VHS tape
which got badly mangled in an old VHS machine making the tape unplayable, so
as an experiment I took a good bit of the tape near the end and wound it
upside down on the take-up spool, and then sorted out the supply spool in
the same way before putting it back into the cassette. And when I played it,
the picture was upside down - as expected, really.

Do PVRs actually display subtitles if you play a recording slowly or
backwards?

In message <sshth3$o3e$1@dont-email.me>, NY <me@privacy.invalid> writes

>
>Do PVRs actually display subtitles if you play a recording slowly or
>backwards?

Just checked. My Manhattan satellite PVR does. It displays the subtitles
at what looks like the appropriate times.
--
Ian

On 22/01/2022 21:08, Woody wrote:
> On Sat 22/01/2022 21:02, williamwright wrote:
>> OK you wise guys! How come, when I play a programme backwards on the
>> PVR, the subtitles aren't written backwards?
>>
>> Seamus
>
> You are only showing the movement in reverse, the picture isn't reversed
> is it?
>
> So why should the subtitles be backwards?

If there was sound they'd have to be saying everything backwards.

Bill

Ian Jackson wrote:

>Just checked. My Manhattan satellite PVR does. It displays the subtitles
>at what looks like the appropriate times.

They can be pretty variable even going forwards. :-(

On my Humax some channels always seem to have poor
synchronisation with the subtitles. More4 is a particular
offender.

Chris
--
Chris J Dixon Nottingham UK
chris@cdixon.me.uk @ChrisJDixon1

Plant amazing Acers.

That is just silly.
You are still picking up the frames from start to end so the data is still
the same.
Back in the days of Vcrs, who recalls the old problem of those Phillips
tapes getting a little crease in the bottom edge, and jamming. If you had an
old hub set from a chewed one handy, simply make the tape upside down and it
could work pretty well, but when played back if not recorded over, you could
sometimes see the picture upside down, even though it was scanning the
tracks across them getting bits of multiple tracks. No sync since the track
was now playing on the audio channel and vice versa and the colours were all
over the place.
Great fun, and really I was surprised the system actually managed to get
anything considering the slanted azimuth of the heads on the 1700 machines.
Brian

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"williamwright" <wrightsaerials@f2s.com> wrote in message
news:j539n6F32doU1@mid.individual.net...
> OK you wise guys! How come, when I play a programme backwards on the PVR,
> the subtitles aren't written backwards?
>
> Seamus

If there was sound is a big clue. What you might get is a garbeled mess, not
backwards. The data is still there but they are just bits of data and would
not make any sense if you allowed them to be played.

The picture works as it is actually read to a buffer a chunk at a time which
tends to be a frame sized one.

Brian

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"williamwright" <wrightsaerials@f2s.com> wrote in message
news:j540kgF72ucU1@mid.individual.net...
> On 22/01/2022 21:08, Woody wrote:
>> On Sat 22/01/2022 21:02, williamwright wrote:
>>> OK you wise guys! How come, when I play a programme backwards on the
>>> PVR, the subtitles aren't written backwards?
>>>
>>> Seamus
>>
>> You are only showing the movement in reverse, the picture isn't reversed
>> is it?
>>
>> So why should the subtitles be backwards?
>
> If there was sound they'd have to be saying everything backwards.
>
> Bill

Brian Gaff \(Sofa\) <briang1@blueyonder.co.uk> wrote:
> That is just silly.
> You are still picking up the frames from start to end so the data is still
> the same.
> Back in the days of Vcrs, who recalls the old problem of those Phillips
> tapes getting a little crease in the bottom edge, and jamming. If you had an
> old hub set from a chewed one handy, simply make the tape upside down and it
> could work pretty well, but when played back if not recorded over, you could
> sometimes see the picture upside down, even though it was scanning the
> tracks across them getting bits of multiple tracks. No sync since the track
> was now playing on the audio channel and vice versa and the colours were all
> over the place.
> Great fun, and really I was surprised the system actually managed to get
> anything considering the slanted azimuth of the heads on the 1700 machines.
> Brian
>

Actually, is playing a digital stream backwards straightforwards? My basic
understanding is you create some sort of master frame that contains the
whole picture and then a series of deltas thereafter and then another
master. If you play backwards you get the deltas first. So does the decoder
have to play small chunks forwards internally to reconstruct something it
can play in reverse? Never really thought about it before.

On Sun, 23 Jan 2022 09:58:07 -0000 (UTC), Tweed <usenet.tweed@gmail.com>
wrote:

> Actually, is playing a digital stream backwards straightforwards? My basic
> understanding is you create some sort of master frame that contains the
> whole picture and then a series of deltas thereafter and then another
> master. If you play backwards you get the deltas first. So does the decoder
> have to play small chunks forwards internally to reconstruct something it
> can play in reverse? Never really thought about it before.

One presumes it has to create the entire GoP in memory, but it's doing
that whilst playing forwards as well.

There is really no concept of backwards, its merely data and the software
one supposes packages the data in a readable form in the first place, so
there should be no issue. Brian

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"Paul Ratcliffe" <abuse@orac12.clara34.co56.uk78> wrote in message
news:slrnsus03t.mko.abuse@news.pr.network...
> On Sun, 23 Jan 2022 09:58:07 -0000 (UTC), Tweed <usenet.tweed@gmail.com>
> wrote:
>
>> Actually, is playing a digital stream backwards straightforwards? My
>> basic
>> understanding is you create some sort of master frame that contains the
>> whole picture and then a series of deltas thereafter and then another
>> master. If you play backwards you get the deltas first. So does the
>> decoder
>> have to play small chunks forwards internally to reconstruct something it
>> can play in reverse? Never really thought about it before.
>
> One presumes it has to create the entire GoP in memory, but it's doing
> that whilst playing forwards as well.

"Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
news:sslpke$3l1$1@dont-email.me...
> There is really no concept of backwards, its merely data and the software
> one supposes packages the data in a readable form in the first place, so
> there should be no issue. Brian

I suppose if you wanted to get really picky, the data stream can't be read
backwards correctly because the least-significant bit would arrive first and
the most-significant bit would arrive last (or vice-versa), and the frame
headers would be at the end rather than the beginning of the frame that they
applied to. You'd also receive the incremental "difference" frames before
the full frame that they related to.

Assuming that the software was able to reverse all this and interpret it
correctly, then as you say you'd accumulate a buffer of a few frames that
actually made sense as a complete GoP, even if the buffer was filled with
bytes that arrived in the opposite order to normal. And that buffer could
then be played out with frames in reverse order. This is what applications
such as VLC and the firmware in dedicated PVRs do.

On 24/01/2022 08:56, Brian Gaff (Sofa) wrote:
> There is really no concept of backward

They don't even say 'educationally sub-normal' nowadays.

Bill

On 24/01/2022 09:32, NY wrote:
> "Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
> news:sslpke$3l1$1@dont-email.me...
>> There is really no concept of backwards, its merely data and the
>> software one supposes packages the data in a readable form  in the
>> first place, so there should be no issue. Brian
>
> I suppose if you wanted to get really picky, the data stream can't be
> read backwards correctly because the least-significant bit would arrive
> first and the most-significant bit would arrive last (or vice-versa),
> and the frame headers would be at the end rather than the beginning of
> the frame that they applied to. You'd also receive the incremental
> "difference" frames before the full frame that they related to.

When playing backwards or a recording faster forward are only the
reference (full) frames displayed?

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

"alan_m" <junk@admac.myzen.co.uk> wrote in message
news:j58ar5F20p8U1@mid.individual.net...
> On 24/01/2022 09:32, NY wrote:
>> "Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
>> news:sslpke$3l1$1@dont-email.me...
>>> There is really no concept of backwards, its merely data and the
>>> software one supposes packages the data in a readable form in the first
>>> place, so there should be no issue. Brian
>>
>> I suppose if you wanted to get really picky, the data stream can't be
>> read backwards correctly because the least-significant bit would arrive
>> first and the most-significant bit would arrive last (or vice-versa), and
>> the frame headers would be at the end rather than the beginning of the
>> frame that they applied to. You'd also receive the incremental
>> "difference" frames before the full frame that they related to.
>
> When playing backwards or a recording faster forward are only the
> reference (full) frames displayed?

I suppose it depends on the speed of fast playback. If you only played the
reference frames, you'd be going at about 15x normal speed, assuming a GoP
of about 15 frames. Many PVRs offer a range of speeds ranging from as low as
2x up to about 30x. I imagine that they choose to display every nth frame
(where n is controllable) which in practice will involve reference frames
always being decoded and then the required intermediate frames being
calculated wrt to the previous reference frame so all the required frames
(intermediate or reference) are available.

I've not got an HD PVR (I record on a Raspberry Pi running TVHeadend and
watch using VLC on my PC or else via Plex on a TV) so I wonder if the
playback capabilities in HD are more limited or more jerky (ie fewer
different frames per second, with some being repeated) because H264 is a lot
more computationally intensive than MPEG to decode.

No It used to be Intellectually challenged but I think even that has moved
on to Neurologically diverse.
Brian

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"williamwright" <wrightsaerials@f2s.com> wrote in message
news:j58a57F1qlqU1@mid.individual.net...
> On 24/01/2022 08:56, Brian Gaff (Sofa) wrote:
>> There is really no concept of backward
>
> They don't even say 'educationally sub-normal' nowadays.
>
> Bill

On Mon, 24 Jan 2022 20:55:05 -0000, NY <me@privacy.invalid> wrote:

> I've not got an HD PVR (I record on a Raspberry Pi running TVHeadend and
> watch using VLC on my PC or else via Plex on a TV) so I wonder if the
> playback capabilities in HD are more limited or more jerky

Mine seems the same on HD as on SD (not that I watch much of the latter).

> because H264 is a lot more computationally intensive than MPEG to decode.

It's all done in hardware either way. 'Trivial' these days.

On 22/01/2022 21:02, williamwright wrote:
> OK you wise guys! How come, when I play a programme backwards on the
> PVR, the subtitles aren't written backwards?

Duh!

What does happen?

I don't think my PVR shows any subtitles when playing backwards.

--
Brian Gregory (in England).

On 22/01/2022 09:38 pm, NY wrote:
> "Woody" <harrogate3@ntlworld.com> wrote in message
> news:sshrpb$bs8$1@dont-email.me...
>> On Sat 22/01/2022 21:02, williamwright wrote:
>>> OK you wise guys! How come, when I play a programme backwards on the
>>> PVR, the subtitles aren't written backwards?
>>>
>>> Seamus
>>
>> You are only showing the movement in reverse, the picture isn't
>> reversed is it?
>>
>> So why should the subtitles be backwards?
>
> If you load a VHS video tape upside down (by unreeling it and winding it
> the opposite way on the spools) the picture is upside down, as well as
> being very ragged because the sync pulses are in the wrong place. I had
> a VHS tape which got badly mangled in an old VHS machine making the tape
> unplayable, so as an experiment I took a good bit of the tape near the
> end and wound it upside down on the take-up spool, and then sorted out
> the supply spool in the same way before putting it back into the
> cassette. And when I played it, the picture was upside down - as
> expected, really.
>
> Do PVRs actually display subtitles if you play a recording slowly or
> backwards?

I can certainly arrange the phenomenon you describe, but only after
copying from (say) a Sky box with subtitles switched in.