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Old 12-06-2012, 05:19 PM   #1
misterclick
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Paused video moving?

When I press pause on one tuner and go to the next one and watch something or look at what is playing, when I go back to the other tuner the "paused" screen has moved! Maybe just a couple of seconds, or so, or sometimes it's in the next scene. At first I thought it was just my imagination, but now I know it happens. Does anyone know why it does it? Could there be a problem coming? Click
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Old 12-06-2012, 05:31 PM   #2
waynomo
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Originally Posted by misterclick View Post
When I press pause on one tuner and go to the next one and watch something or look at what is playing, when I go back to the other tuner the "paused" screen has moved! Maybe just a couple of seconds, or so, or sometimes it's in the next scene. At first I thought it was just my imagination, but now I know it happens. Does anyone know why it does it? Could there be a problem coming? Click
No problem. Your TiVo HD is reading from a specific point on the disc. You press pause and then switch to the other tuner. You are not really watching from the tuner. The program is being written to disc first. So now you are reading from another area of the disc. When you press the "Live TV" button to change back to the other tuner, you are really just accessing another part of the disc. It doesn't remember the exact spot where you were, but a segment. Doing this instead of having to index every frame of video makes switching quicker.
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Old 12-06-2012, 06:36 PM   #3
misterclick
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Mmmm the explanation sounds good, except that it had never happened before! Was this part of a software upgrade? Changed setting? Hard drive getting close to being filled?
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Old 12-07-2012, 02:15 PM   #4
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This has always happened with me...not really a problem....but it's interesting.
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Old 12-07-2012, 04:22 PM   #5
Dan203
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Originally Posted by waynomo View Post
No problem. Your TiVo HD is reading from a specific point on the disc. You press pause and then switch to the other tuner. You are not really watching from the tuner. The program is being written to disc first. So now you are reading from another area of the disc. When you press the "Live TV" button to change back to the other tuner, you are really just accessing another part of the disc. It doesn't remember the exact spot where you were, but a segment. Doing this instead of having to index every frame of video makes switching quicker.
That's not quite right. The problem here is caused by the temporal compression used by MPEG-2. MPEG-2 video can only start decoding on an I frame. The frequency of I frames in the original video stream is determined by the GOP size set during encoding. Can be anywhere from one every 1/2 second to one every 2-3 seconds. When you pause a recording it shows the exact frame you were on, even if it's a P or B frame, because it has decoded the video to that point and is capable of displaying that frame. However when you switch tuners you flush the decode buffer which means the frame you were displaying can no longer be decoded. So when you switch back to that tuner it has to jump to the nearest I frame to start decoding again. There are a few things that can mess up that jump. First if the GOPs are really long then the nearest I frame might be 2-3 seconds away from where you were paused. Second there is no map telling the software where exactly the nearest I frame is, so they have to guess. If it's anything like VideoReDo they guess by using the average bitrate of the entire stream. However if the bitrate fluctuates a lot over the course of the stream it can throw off that guess.

In any case you were right that it's no problem.

OP - The reason you're likely just starting to see this is because a lot of cable companies and networks have started adjusting their encoding parameters to save bandwidth. These changes usually include using longer GOPs and more variable bitrates, both of which can effect the pause point as mentioned above. Unlike the old S2 TiVos the HD units record the MPEG-2 stream as-is, so they don't have any control over the encoding parameters and have to deal with what they get as best they can.

Dan
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Old 12-07-2012, 05:54 PM   #6
misterclick
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Thank you Dan, that makes perfect sense I was going to mention that my S2 did not do it at all, but I didn't think of mentioning since the video is of a different quality. And you're right, it keeps happening more and more, when I first got the unit about 2 years ago this problem did not exist. Now I know. Click

I like your signature, but I always thought it was:

"It's all fun and games until someone loses a nut" - Squirrels
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Old 12-07-2012, 06:50 PM   #7
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My signature is a direct quote from by wife, who use to be a member here named loopey. (we actually met via this forum) She said that to me one day, completely serious, and I just laughed. I put it as my signature as sort of a rib on her. That was like 10 years ago and I've never changed it.

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Old 12-10-2012, 11:29 AM   #8
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Good for you! Thanks for sharing...
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