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Old 05-05-2012, 05:00 PM   #1
MizzouDan
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Tivo Premiere File Sizes Shrinking after Cable System Upgrade

I have both a Tivo Series 2 and a Tivo Premiere.

My cable company recently upgraded their infrastructure out of the 1980s and into the present day. But something strange has happened as a result.

My Tivo Series 2 is behaving exactly as it had been behaving before the upgrade.

But my Tivo premier is doing something I don't understand.

I often make redundant recordings with the two boxes- same recording quality (Best), and same length, channel, etc. Before the upgrade, the same recording on my Premiere would generally be about 10-15% larger in terms of file size than it's Series 2 counterpart. After the upgrade, an identical recording on the premiere will only be about 70-75% as large as the series 2 counterpart.

The recordings on the Series 2 seem to be about the same size as they've always been at a given length and quality. The Premiere recordings are only a little over half they sizes they used to be. I verified to make sure my default quality was set at "Best," and it is.

Another thing that may or may not be related: I often transfer the recordings to Tivo Desktop and then edit them with VideoRedo software. When I transfer from my Series2, the file behaves normally during editing. When I transfer from the premiere, the software has trouble syncing the frames on playback with the frames in the frame-by-frame navigation system. In other words, it won't show the correct picture in the navigator that it shows on the viewing module. It will also get stuck in loops where I can't advance or reverse the navigation more than a few frames unless I actually hit play. I have a feeling this will make no sense unless you use VideoRedo like I do. When I perform a Quickstream Fix, the video then begins behaving normally. The Sync issue (but not the navigation loop) used to happen sometimes before the upgrade, but it now happens every single time I try to edit a Premiere recording, plus the loop now occurs.

Strangely, I haven't noticed any significant loss of video or audio quality in the apparently undersized recordings. That being said, I'm not enough of a techie to necessarily recognize subtle differences. Could it be that my cablecard is receiving at a lower bitrate or resolution than my cable box? Or is this just a case where my Series 2 could be trying to record at a higher quality than the source is capable of delivering, and thus inflating its file sizes artificially?

As a point of reference, my Series 2 last night recorded an hour and 45 minute program at best quality at a size of 4718 MB. The Premiere recorded the same program with the same specs at 3400 MB. Before the upgrade, I would have expected the latter number to be at or above 5000 MB.

I talked to Tivo Support about this for a very long time, but the guy was pretty unhelpful. He kept obsessing over the fact that the Series 2 has an expanded hard drive, which isn't really relevant considering the file sizes haven't changed on it at all, and are consistent with what my prior, unmodified Series 2 was doing.

Also, he had me check the disk usage for the program referenced above. For some reason it showed up on my series 2 as 4.2 GB, but only .03 GB on my Premiere. This seems like a mistake- whether it just displays wrong on the Premiere or if there's something really screwed up with the internal workings of the thing. That's only like 30 megs, and yet I still have a solid quality 105 minutes of video out of it.

Any help or advice would be much appreciated. I just can't trust these small files to be high quality, even though they appear to be, without some understanding of why they're turning out that way.
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Old 05-05-2012, 05:19 PM   #2
compnurd
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I would say one of two things, either your cable company is compressing the hell out of the signal, or they are using MPEG4 or H.264. You can check your cable signal settings, it will tell you the format. most companies are MPEG2 but some have slowy started the upgrade to MPEG 4
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Old 05-05-2012, 09:26 PM   #3
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Sounds like before the upgrade those channels were analog and were being encoded by your TiVo from an analog signal. Now they're being simulcast in digital and your Premiere is automatically selecting the digital channel and saving them already encoded by your cable company, which is normally a better compression.
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Old 05-05-2012, 09:38 PM   #4
crxssi
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Quote:
Originally Posted by MizzouDan View Post
I often make redundant recordings with the two boxes- same recording quality (Best), and same length, channel, etc. Before the upgrade, the same recording on my Premiere would generally be about 10-15% larger in terms of file size than it's Series 2 counterpart. After the upgrade, an identical recording on the premiere will only be about 70-75% as large as the series 2 counterpart.
As has been said, either they are dropping the bitrate of the programs (by transcoding them), which is sucky, they have switched the stations you are recording from mpeg2 to the H.264 codec, or you have just jumped from analog in to digital in and your Premiere is no longer having to encode/digitize/record the video any longer.

Quote:
Another thing that may or may not be related: I often transfer the recordings to Tivo Desktop and then edit them with VideoRedo software. When I transfer from my Series2, the file behaves normally during editing. When I transfer from the premiere, the software has trouble syncing the frames on playback with the frames in the frame-by-frame navigation system. In other words, it won't show the correct picture in the navigator that it shows on the viewing module.
I know nothing about "VideoRedo" because it doesn't run in Linux. But what you are describing is a video editing program that is apparently having problems reconstituting the video due to unexpected yet needed frames. http://en.wikipedia.org/wiki/Video_c..._picture_types

This is more evidence that they did change the encoding on your cable system. Your software might be, for example, expecting more Index (I) frames than are present. It can't (for whatever reason) reconstitute some of the video, ad-hoc, from the remaining B or P frames.

Quote:
Also, he had me check the disk usage for the program referenced above. For some reason it showed up on my series 2 as 4.2 GB, but only .03 GB on my Premiere. This seems like a mistake- whether it just displays wrong on the Premiere or if there's something really screwed up with the internal workings of the thing. That's only like 30 megs, and yet I still have a solid quality 105 minutes of video out of it.
That is a known bug if you are using SDUI: http://www.tivocommunity.com/tivo-vb...d.php?t=481338 4.2

Move the decimal two places to the left. It is 3GB.
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Old 05-06-2012, 04:46 AM   #5
BigJimOutlaw
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Quote:
Originally Posted by nrc View Post
Sounds like before the upgrade those channels were analog and were being encoded by your TiVo from an analog signal. Now they're being simulcast in digital and your Premiere is automatically selecting the digital channel and saving them already encoded by your cable company, which is normally a better compression.
This would be my first guess also... The Premiere is now recording a digital channel instead of an analog one. I noticed the same thing back when I switched TV carriers and went all-digital.

Or, if the previous Premiere recordings were digital for sure, the cableco likely altered their digital broadcast (compressed it) to fit more channels into the same amount of bandwidth.

Last edited by BigJimOutlaw : 05-06-2012 at 04:53 AM.
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