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A 2010 compendium of D* DVR bugs


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#151 OFFLINE   Rich

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Posted 26 May 2010 - 02:33 PM

VCRs had basically linear recording. 30 seconds always equalled the same number of feet of tape. With MPEG encoding, 30 seconds could be 100k of data or 100MB, and the encoding is variable.


Well, let me go find out what encoding means in this context...

Rich

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#152 OFFLINE   Steve

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Posted 26 May 2010 - 02:50 PM

Well, let me go find out what encoding means in this context...

Shows with scenes that change rapidly from frame to frame can not be compressed as efficiently as news broadcasts, e.g., where the "talking heads" sit in front of a desk and a static background. If the camera doesn't move, the desk and background can be "re-used" for several frames, and only the broadcasters need to be recompressed every frame because they're moving.

Much like a noisy, grainy photograrph taken at high ISO will save as a larger jpeg than the same scene taken with flash at a lower ISO that exhibits less "grain". Large patches of solid color, like blue skies, compress very efficiently.
/steve

#153 OFFLINE   Syzygy

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Posted 26 May 2010 - 05:22 PM

I tested :30 second skip on my HR24-500 via an on screen timer...it was spot on.

I switched to 30SLIP for testing and found that "30-second slip" always slips between 32 and 33 seconds. I used the HDNet test pattern [HD] to time it.
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#154 OFFLINE   Mike Bertelson

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Posted 26 May 2010 - 06:50 PM

And yet, VCRs had it down pat. At least the Sonys did. I watched a lot of fights and when the bell rang at the end of a round, you hit the skip button however many times for one minute and it coincided with the next round's beginning bell. Not a big deal, only time I notice it is on fights, but I've never seen a post about it. Curious.

Rich

30 seconds of tape in an exact amount of tape. It’s linear and very easy to do. However, 30 seconds of data is subject to many different variables.

Now my old Panasonic VCR would mark the start and end of each set of commercials, and automatically skip them when you started watching the program. Now that would be cool. :D

Mike

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#155 OFFLINE   Steve

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Posted 26 May 2010 - 06:55 PM

[...]Now my old Panasonic VCR would mark the start and end of each set of commercials, and automatically skip them when you started watching the program. Now that would be cool. :D [...]

The Replay DVR did that at first and really ticked off the studios. I think if they auto-FF'd instead of auto-skipped, they might have had less resistance, since that what users do anyway.
/steve

#156 OFFLINE   drpjr

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Posted 26 May 2010 - 08:26 PM

I suspect it's related to the type of material and what else the system is doing at that point in time. Of course that's only a guess.

At any rate, I'm not sure it's possible to make it exactly 30 seconds all the time...I've been wrong before. :grin:

Mike

I trust your guess as I am in the deep end of the pool in this discussion.:lol:

VCRs had basically linear recording. 30 seconds always equalled the same number of feet of tape. With MPEG encoding, 30 seconds could be 100k of data or 100MB, and the encoding is variable.


Feet of tape or frames per second , isn't it a fixed amount? Ex: If something is broadcast in 720p/30fps every 900 frames should be 30sec no matter how much encoding was required for each frame or which 900 frames you choose. I guess my question is does the HDDVR count fps to skip/slip? And if it doesnt what does it use? I really find this interesting but am pretty much lost.:confused::lol:
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#157 OFFLINE   Mike Bertelson

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Posted 27 May 2010 - 03:17 AM

I trust your guess as I am in the deep end of the pool in this discussion.:lol:


Feet of tape or frames per second , isn't it a fixed amount? Ex: If something is broadcast in 720p/30fps every 900 frames should be 30sec no matter how much encoding was required for each frame or which 900 frames you choose. I guess my question is does the HDDVR count fps to skip/slip? And if it doesnt what does it use? I really find this interesting but am pretty much lost.:confused::lol:

Does a DVR track frame rates or does it treat it simply as data?

In order to use fps, it would have to track frame rates as well as everything it does. Ok, I have know idea how to do that but I would think it would be much more difficult than simply treating a programs as a computer file.

Mike

µß
Since it costs 1.66¢ to produce a penny, my 2¢ worth is really 3.32¢ worth.  That 3.32¢ is my own and not the 3.32¢ of DIRECTV, Dish, or anyone else for that matter.


#158 OFFLINE   Rich

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Posted 27 May 2010 - 08:15 AM

Shows with scenes that change rapidly from frame to frame can not be compressed as efficiently as news broadcasts, e.g., where the "talking heads" sit in front of a desk and a static background. If the camera doesn't move, the desk and background can be "re-used" for several frames, and only the broadcasters need to be recompressed every frame because they're moving.

Much like a noisy, grainy photograrph taken at high ISO will save as a larger jpeg than the same scene taken with flash at a lower ISO that exhibits less "grain". Large patches of solid color, like blue skies, compress very efficiently.


Thanx, Steve. What I was watching was the between rounds conversation between talking heads.

Rich

#159 OFFLINE   Rich

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Posted 27 May 2010 - 08:21 AM

30 seconds of tape in an exact amount of tape. It’s linear and very easy to do. However, 30 seconds of data is subject to many different variables.

Now my old Panasonic VCR would mark the start and end of each set of commercials, and automatically skip them when you started watching the program. Now that would be cool. :D

Mike


I had one of those VCRs too. Didn't work very well, but a good idea that we'll never see implemented again. For obvious reasons.

By the way, think back to how precise the electronics were on your sub. My destroyer's electronics were so precise it amazed me. And that was a long time ago. And for you folks who might not believe it, we had digital electronics way back then. I'd love to get on one of the new destroyers and see what kind of goodies they have now. Must be mind blowing. And years ahead of what we see in stores today.

Rich

#160 OFFLINE   Rich

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Posted 27 May 2010 - 08:26 AM

I trust your guess as I am in the deep end of the pool in this discussion.:lol:


Feet of tape or frames per second , isn't it a fixed amount? Ex: If something is broadcast in 720p/30fps every 900 frames should be 30sec no matter how much encoding was required for each frame or which 900 frames you choose. I guess my question is does the HDDVR count fps to skip/slip? And if it doesnt what does it use? I really find this interesting but am pretty much lost.:confused::lol:


Well, we're lost together. We can blow up a house in Berzerkistan from a console in California, but we can't measure 30 seconds accurately on a DVR? Oh well, I really didn't mean to start an argument, just commenting on an ongoing MINOR annoyance, but now I'm with you, befuddled again. :lol:

Rich

#161 OFFLINE   Steve

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Posted 27 May 2010 - 08:32 AM

Does a DVR track frame rates or does it treat it simply as data? [...]

Video is encoded to a frame rate, but I believe trickplay always needs to land on a "key" frame, which is the first frame in a sequence of frames that whatever compression is being used determines is most important to encode with as little loss of quality as possible.

That's why it sometimes appears after stopping FFX1, which has no autocorrection applied to it, that the video still jumps backwards before resuming play. I believe that happens when the closet key frame to the stopping point is before the resume point, and the HR needs to "back-up" to find it. Otherwise, if it always jumped to the next keyframe, there would be a risk of a dropped word of dialog.

MPEG-2 by it's nature is encoded with more key frames than MPEG-4, which is why MPEG-2 file sizes are larger. As a result, tho, MPEG-2 trickplay is smoother.

I think trickplay is an area where the HR's were being unfairly compared to the DirecTiVo, because the HR10 only had to deal with MPEG-2 files. Comparing MPEG-2 to MPEG-4 trickplay is really comparing apples to oranges.
/steve

#162 OFFLINE   Syzygy

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Posted 27 May 2010 - 03:45 PM

MPEG-2 by it's nature is encoded with more key frames than MPEG-4, which is why MPEG-2 file sizes are larger. As a result, tho, MPEG-2 trickplay is smoother.

I think trickplay is an area where the HR's were being unfairly compared to the DirecTiVo, because the HR10 only had to deal with MPEG-2 files. Comparing MPEG-2 to MPEG-4 trickplay is really comparing apples to oranges.

As I recall, trick play on my HR21 behaved the same with the rare MPEG-2 recording as it did with MPEG-4.

Are there any MPEG-2 channels left for an HR2x to experiment with? T101, say?
Frank TiVangelist since Aug 1999, HD since Dec 2002, DirecTV since Aug 2004, DECA/MRV since Nov 2010
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#163 OFFLINE   LameLefty

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Posted 27 May 2010 - 03:48 PM

As I recall, trick play on my HR21 behaved the same with the rare MPEG-2 recording as it did with MPEG-4.

Are there any MPEG-2 channels left for an HR2x to experiment with? T101, say?


Record a local OTA.

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#164 OFFLINE   Steve

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Posted 27 May 2010 - 04:33 PM

As I recall, trick play on my HR21 behaved the same with the rare MPEG-2 recording as it did with MPEG-4 [...]

You haven't watched enough MPEG-2 then. :) As Lefty says, try an OTA recording. Trickplay is smooth as silk. I record NFL games OTA whenever possible for just that reason.
/steve

#165 OFFLINE   drpjr

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Posted 27 May 2010 - 07:57 PM

Well, we're lost together. We can blow up a house in Berzerkistan from a console in California, but we can't measure 30 seconds accurately on a DVR? Oh well, I really didn't mean to start an argument, just commenting on an ongoing MINOR annoyance, but now I'm with you, befuddled again. :lol:

Rich


Befuddled? Can I get an Amen Brother?:D This is something I would never have noticed on my own. Good catch by the way. It reminds me of the picture intermittantly flashing through the screensaver, it doesn't effect function and it doesn't bother me in the least, but I want to know why it does it. After reading Steve's explanation I feel that I have a pretty good grasp of the concepts involved. I just keep coming up with a bunch of "yeah...but" questions.:lol:
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#166 OFFLINE   Mike Bertelson

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Posted 27 May 2010 - 08:42 PM

Well, we're lost together. We can blow up a house in Berzerkistan from a console in California, but we can't measure 30 seconds accurately on a DVR? Oh well, I really didn't mean to start an argument, just commenting on an ongoing MINOR annoyance, but now I'm with you, befuddled again. :lol:

Rich

I’m guessing here, but I think it has little to do with "can't" and more to do with the amount of work for so little a benefit. How much coding and how many more modules would you need to add to the firmware to get exactly 30 seconds vs. 30-33 seconds? Is it really worth it to do all that work when, for 99%, of users, the extra 1-3 seconds isn’t really going to matter? IMHO, I would say no as I feel there are much more important things to spend time and lines of code on.

My 2¢ FWIW. :)

Mike

µß
Since it costs 1.66¢ to produce a penny, my 2¢ worth is really 3.32¢ worth.  That 3.32¢ is my own and not the 3.32¢ of DIRECTV, Dish, or anyone else for that matter.


#167 OFFLINE   bonscott87

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Posted 27 May 2010 - 08:43 PM

As I recall, trick play on my HR21 behaved the same with the rare MPEG-2 recording as it did with MPEG-4.

Are there any MPEG-2 channels left for an HR2x to experiment with? T101, say?


Yep, MPEG2 on an HR2x is just as smooth as the DirecTivo. Trickplay "choppiness" is due to MPEG4. Almost a guarantee that this new DirecTivo will have the same issue. Just a nature of the technology.

#168 OFFLINE   Syzygy

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Posted 27 May 2010 - 09:03 PM

Are there any MPEG-2 channels left for an HR2x to experiment with? T101, say?

Record a local OTA.

As Lefty says, try an OTA recording.

Sorry, I can't. Not all of us have OTA tuners (HR20 or AM21). ;)
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#169 OFFLINE   Syzygy

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Posted 27 May 2010 - 09:04 PM

Yep, MPEG2 on an HR2x is just as smooth as the DirecTivo. Trickplay "choppiness" is due to MPEG4. Almost a guarantee that this new DirecTivo will have the same issue. Just a nature of the technology.

OK, I believe. Too bad, tho.
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#170 OFFLINE   Syzygy

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Posted 27 May 2010 - 09:12 PM

I switched to 30SLIP for testing and found that "30-second slip" always slips between 32 and 33 seconds. I used the HDNet test pattern [HD] to time it.

I switched back to 30SKIP and (again with the HDNet test pattern) found that one "30-second skip" always skips between 31 and 32 seconds, while a group of skips covers less time than expected; each successive skip tacked onto the chain of skips goes forward about 28 seconds.

Conclusions:
1. SLIP's extra 2 or 3 seconds (5 or 6 seconds in another report) is mainly due to slugglish response (which seems to affect each SLIP in a chain of SLIPs).
2. SKIP's nearly-correct timing (for a single keypress) is the result of combining a programmed amount of around 28 seconds with the somewhat variable slugglishness. However, succeeding SKIPs in a chain are shorter because the slugglishness (latency) has little or no effect on them.
3. The average duration of a "30-second" SKIP can provide a rough estimate of a particular unit's latency.

Edited by Syzygy, 28 May 2010 - 04:17 PM.

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#171 OFFLINE   Rich

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Posted 28 May 2010 - 07:33 AM

Video is encoded to a frame rate, but I believe trickplay always needs to land on a "key" frame, which is the first frame in a sequence of frames that whatever compression is being used determines is most important to encode with as little loss of quality as possible.

That's why it sometimes appears after stopping FFX1, which has no autocorrection applied to it, that the video still jumps backwards before resuming play. I believe that happens when the closet key frame to the stopping point is before the resume point, and the HR needs to "back-up" to find it. Otherwise, if it always jumped to the next keyframe, there would be a risk of a dropped word of dialog.

MPEG-2 by it's nature is encoded with more key frames than MPEG-4, which is why MPEG-2 file sizes are larger. As a result, tho, MPEG-2 trickplay is smoother.

I think trickplay is an area where the HR's were being unfairly compared to the DirecTiVo, because the HR10 only had to deal with MPEG-2 files. Comparing MPEG-2 to MPEG-4 trickplay is really comparing apples to oranges.


That does make it much clearer. I've been getting some long jump backs that look like auto-correction and I thought that was due to having the Ethernet MRV setup. Sometimes it jumps back a minute or two. Rather disconcerting when you don't know what's causing it. I feel better knowing it's normal. Normal I can deal with. :)

Rich

#172 OFFLINE   Rich

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Posted 28 May 2010 - 07:44 AM

Befuddled? Can I get an Amen Brother?:D This is something I would never have noticed on my own. Good catch by the way. It reminds me of the picture intermittantly flashing through the screensaver, it doesn't effect function and it doesn't bother me in the least, but I want to know why it does it. After reading Steve's explanation I feel that I have a pretty good grasp of the concepts involved. I just keep coming up with a bunch of "yeah...but" questions.:lol:


Sometime in Steve's life he must have learned that to reach people with information that they can comprehend you have to get down to a level that they can understand. His posts have always been clear and (relatively) easy to understand.

If you want everyone to understand the message, you must get down to a fifth or sixth grade level. For the younger generations who don't read I don't know how far down you'd have to go. That's not an insult aimed at younger folks, that's an indictment of our school systems. Just go to any school and ask the students if they've read Moby Dick. I did this many times while my son (who never read it) was growing up and found one person who had read it. And he was from Sierra Leone. But, they've all seen the movies. :)

Rich

#173 OFFLINE   Rich

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Posted 28 May 2010 - 07:48 AM

I’m guessing here, but I think it has little to do with "can't" and more to do with the amount of work for so little a benefit. How much coding and how many more modules would you need to add to the firmware to get exactly 30 seconds vs. 30-33 seconds? Is it really worth it to do all that work when, for 99%, of users, the extra 1-3 seconds isn’t really going to matter? IMHO, I would say no as I feel there are much more important things to spend time and lines of code on.

My 2¢ FWIW. :)

Mike


I can't really think of anything but fights where you'd notice the inaccuracy of the slip and, as I said, it's really a minor annoyance. And it's easily correctable with a quick jump back. If the TS hadn't started this thread, I would never have commented on it.

Rich

#174 OFFLINE   Steve

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Posted 28 May 2010 - 08:08 AM

That does make it much clearer. I've been getting some long jump backs that look like auto-correction and I thought that was due to having the Ethernet MRV setup. Sometimes it jumps back a minute or two. Rather disconcerting when you don't know what's causing it. I feel better knowing it's normal. Normal I can deal with. :)

I do want to say that what I was talking about (finding a key frame) only applies to FFX1, where there isn't any intentional autocorrection applied, AFAIK, and searching for a key frame sometimes takes you backwards a second or two.

If autocorrection seems too long on FFX2 or FFX3, that may be either because your reflexes are above the average user for which they calculated what the correction time should be, or the s/w release you're on may be beta or still needs to be tuned better for local vs. MRV autocorrect. I generally don't see autocorrect issues, because I'm a 30-skipper. I use that to get past MRV commercials and it works flawlessly for me.

Edited by Steve, 28 May 2010 - 08:19 AM.

/steve

#175 OFFLINE   Steve

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Posted 28 May 2010 - 08:17 AM

I switched back to 30SKIP and (again with the HDNet test pattern) found that one "30-second skip" always skips between 31 and 32 seconds, while a group of skips covers less time than expected; each successive skip tacked onto the chain of skips goes forward about 28 seconds [...]

This may be by design, to compensate for "looking" time in between SKIPS. If you're like me, I stack 4-5 right away, and then pause to see where I'm at before clicking SKIP again.
/steve




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