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gbmonster
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freeze frame rears its ugly head

Post by gbmonster »

Hi all, it's been a while!

I've been rummaging around the archives to see if anyone else has managed to put a little time into a tiny tap (I expect) that would sort out the slightly rubbish freeze frame, frame advance things on the toppy.

I'm a film extra so I occasionally want to click through a recording a frame at a time, usually to confirm my two weeks filming has resulted in my elbow making it into shot!

It also has the obvious 'basic instinct' appeal.

I know others have asked in the past, if I knew where to start I'd code it myself... Haven't done any programming in about 15 years now though.

GB x
ryclark
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Post by ryclark »

The problem is that DTT transmissions use fairly large GOPs (Groups Of Frames) in their lossy MPEG2 coding. This means that it is very difficult to produce individual still frames as there is only one complete frame transmitted every 15 or so frames. So a still frame is only produced about every .6 sec. When you are watching the moving pictures the intermediate frames are just built using the information that changes between each I frame (complete image frame).

http://en.wikipedia.org/wiki/Group_of_pictures
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gbmonster
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Post by gbmonster »

[quote="ryclark"]The problem is that DTT transmissions use fairly large GOPs (Groups Of Frames) in their lossy MPEG2 coding. This means that it is very difficult to produce individual still frames as there is only one complete frame transmitted every 15 or so frames. So a still frame is only produced about every .6 sec. When you are watching the moving pictures the intermediate frames are just built using the information that changes between each I frame (complete image frame).

I guessed this was the cause from my generic knowledge of mpeg compression. Thanks for confirming it.

Doesn't this mean though that so long as you are moving FORWARD from a full index frame and maintain the changes in each subsequent bit frame that you should be able to inherently create each frame accurately. Going backwards would be slower at best, impossible at worst as each step backwards would mean going forward from the last index frame to the current frame minus 1; unless that could be done secretly in a buffer and then the output image changed it would be pretty ugly to look at.

Is this level of image control even possible within the SDK or are you limited to tweaking variables?

GB
ryclark
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Post by ryclark »

It also, of course, makes it difficult to do frame accurate video edits hence professional MPEG2 video uses I-frame only compression.
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Laser
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Post by Laser »

The GOP size or pattern is irrelevant to instant pause or frame manipulation. Each frame can and must be decoded as a separate entity in order to display it. (Streams of I-frames help editing because it requires no re-encode to achieve.) Frame advance should be no problem to implement, however frame back could be algorithmically more difficult depending on buffer implementation. DVDs and blu-rays also have GOP sequences and most players offer frame perfect control.

The woeful pause accuracy of the Toppy is far worse than the GOP sizes proposed. Often it is approaching two seconds before a pause is achieved. These permissable pause points are consistent though, so isn't simply control lag.

I wonder if it is to do with audio frame sizes, as the Toppy takes a fair amount of time to sort out playing audio after a pause.

A TAP almost certainly wont have the level of control necessary to achieve an improvement. A firmware patch possibly might, but the people who were most knowledgable about these things seem to no longer be active.
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gbmonster
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Post by gbmonster »

Laser wrote:
A TAP almost certainly wont have the level of control necessary to achieve an improvement. A firmware patch possibly might, but the people who were most knowledgable about these things seem to no longer be active.
That's a shame, the frustrating thing is we're not asking it to do anything clever, just do what it already does ( display each frame clearly) but much more slowly.

That to me sounds like a fairly easy bit of coding but sadly it would take me a week to get something up to even work on! Anyone got a quick quide to toppy firmware fiddling?

GB
juwlz
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Post by juwlz »

gbmonster wrote:Anyone got a quick quide to toppy firmware fiddling?
ROFL. Those that did it had to reverse engineer the code.
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gbmonster
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Post by gbmonster »

juwlz wrote:
gbmonster wrote:Anyone got a quick quide to toppy firmware fiddling?
ROFL. Those that did it had to reverse engineer the code.
That's good then... :-/

You'd think the topfield people would be keen to utilise committed, enthusiastic, and above all free software developers to improve their products.

Shakes head and rolls eyes.
juwlz
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Post by juwlz »

gbmonster wrote:You'd think the topfield people would be keen to utilise committed, enthusiastic, and above all free software developers to improve their products.
They'd already abandoned UK Toppies by July 2008, when the Split NIT issued reared its ugly head. It's only because R2-D2 patched it then that our Toppies weren't all consigned to landfill 6 years ago.

Julie
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gbmonster
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Post by gbmonster »

juwlz wrote:
gbmonster wrote:You'd think the topfield people would be keen to utilise committed, enthusiastic, and above all free software developers to improve their products.
They'd already abandoned UK Toppies by July 2008, when the Split NIT issued reared its ugly head. It's only because R2-D2 patched it then that our Toppies weren't all consigned to landfill 6 years ago.

Julie
Aargh... You mean our beloved toppys are irreplaceable..! Nooooooooooo....



.....



.....some time later....



.....ooooooooooo!

R2-D2... Pass the ball!! :-)
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Post by MikB »

Laser wrote:The GOP size or pattern is irrelevant to instant pause or frame manipulation. Each frame can and must be decoded as a separate entity in order to display it.
Absolutely, it's a matter of how much effort you put into handling it. VideoRedo (software) allows individual frame forward/backward manipulation/editing of the very MPEG stream that Topfield can't handle precise-pause on (in hardware).

When I was at uni, someone's 3rd year project was a basic MPEG editor, with frame accurate edit points, which at the time was pretty hard to get hold of (1994?)

I don't think there's a way to get at the decoded MPEG stream "pictures", other than as done by screen-grab taps. Maybe triggering one of those to grab the screen and overlay it at 100% opacity?

Or, you can access the MPEG stream on disc and software decode it on the Topfield, might be a bit slow though. You'd need to figure out how far in the hardware was, run forward to that point, and decode for a while :(

Wouldn't an upgrade to a VHS recorder be easier? :)
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