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Hi All,


I've read the board for a while before I got my Showstopper, and I must say it's the most informative forum I have ever used.


One thing I haven't found a discussion on however was the ability to advance frames while paused. ( It may be there, I just haven't found it! ) :D


On my Showstopper (v3.00) I can pause a program and then advance by one frame at a time (at least it seems like one frame) by hitting the fast forward button. This is great, however I can not go back any frames by hitting the rewind button. Instead what I get is some hard disk activity and no change on the screen.:confused:


I was wondering if this is by design, a bug in the software, or a defect in my unit. Everything else seems to work fine and I am VERY happy with my new power over TV.


This "problem" however is quite annoying, as if I miss my target, I have to hit play, rewind past the point again, and then pause once more before my original spot.:(


Any insight would be appreciated.

Thanks.
 

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justmike answered this question a while back - something about how hard it was just to get frame by frame to work going forward, he said it was either extremely difficult or impossible (can't remember) to do frame by frame backwards b/c of the mpeg encoder/decoder they used


(something like that)
 

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Tivo claims to have a frame by frame reverse, but it always seems to actually move back at least 2-5 frames to me. May be due to the difficulties mentioned above...
 

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That's because the MPEG encoding results in a full video frame (Key Frame) which is then followed by several "incomplete" frames which only supply the difference between the preceding frame and the current frame. So it's easy to derive a full current frame from the information already present. Going backwards complicates things because you would have to back up to the next previous key frame and then advance to the current frame.
 

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That does make sense! It explains why the number of frames it jumps back doesn't seem to be consistent.
 

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This is a question I've had for a while and it seems topical. Considering mpeg compression has a variable compression ratio, there's no way to predict the file size that a show will produce before recording it. So how do they reserve space for it?

And assuming they use the 'worst-case scenario' for reserving space, if i record an hour of a black screen that results a smaller than expected file size does the unused reserved space become available again after the record takes place?
 

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Quote:
Originally posted by sirak
This is a question I've had for a while and it seems topical. Considering mpeg compression has a variable compression ratio, there's no way to predict the file size that a show will produce before recording it. So how do they reserve space for it?

And assuming they use the 'worst-case scenario' for reserving space, if i record an hour of a black screen that results a smaller than expected file size does the unused reserved space become available again after the record takes place?
Well, the compressors have various options. You can use "variable bit-rate" (VBR) encoding, which will yield (for instance) between 6-8Mbps depending upon the source. Or, you can use a fixed-rate compression that will pretty much deliver 4Mbps no matter what. The ReplayTV's compression is pretty consistent, so it's not very hard to estimate within a couple of percent accuracy. For repeating recordings, the "worst case" is reserved, and remains reserved. If a few meg aren't used by a particular show, then the disk space is available to non-guaranteed recordings. For single recordings, the channel is resized to the actuaal recording size at the conclusion of the recording, so any unused space is fully reclaimed.
 
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