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Looking for a Confirmation, Build 2330 - SVRT reduces the bitrate of the original video
Cap'n Kevin
Senior Contributor Location: Chebeague Island, Maine Joined: Dec 26, 2008 20:22 Messages: 2011 Offline
[Post New]
Hi everyone,

Just wanted to know if this observation seems correct. Does using SVRT reduce the bit rate of the video file when producing to a new video file? Is it supposed to lower it or should it be the same?

I tested a 20 second raw m2ts video from my Sony HDR SR12 video camera with an original bit rate of 16.0 Mbps and when I ran it through SVRT, the resulting file had a bit rate of 15.2 Mbps.

Is that what I should expect?

Can anyone confirm and/or comment on the unexpected results?

I noticed this during beta testing and didn't mention it....probably should have. Maybe if it is not normal it can be added to the list.

Thanks for any input!!

Kevin
 Filename
SVRT Test.txt
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 Description
SVRT MediInfo
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2 Kbytes
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382 time(s)
 Filename
Raw footage.txt
[Disk]
 Description
Raw footage MediaInfo
 Filesize
2 Kbytes
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362 time(s)

This message was edited 1 time. Last update was at Dec 16. 2010 12:45


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Original MTS file -= 15.34 bitrate
Produced M2ts file = 15.55 bitrate (this matches the bitrate in the profile)

[Thumb - svrt.jpg]
 Filename
svrt.jpg
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 Description
SVRT Screen
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138 Kbytes
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This message was edited 7 times. Last update was at Dec 16. 2010 13:56

Cap'n Kevin
Senior Contributor Location: Chebeague Island, Maine Joined: Dec 26, 2008 20:22 Messages: 2011 Offline
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So Fred, your bit rate actually increased when you ran your raw footage through SVRT.

A different result than mine...

Am I the only one that will have this result? It remains to be seen.

By the way....it's not a big deal.....but I thought that SVRT didn't change anything from the original....on my rig...it did.
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The bitrate came from the profile..attempting to modify it (create custom profile) appears to disable SVRT.

This message was edited 1 time. Last update was at Dec 16. 2010 14:00

Cap'n Kevin
Senior Contributor Location: Chebeague Island, Maine Joined: Dec 26, 2008 20:22 Messages: 2011 Offline
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The profile for the AVC h.264 1920X1080 is a default 15500 bit rate.....is that why it is dropping?

Maybe the answer is very simple.....I just didn't think it would drop below that number.

Probably I am just confused by all the numbers...Imagine that!!
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jmone
Senior Contributor Location: Australia Joined: Nov 26, 2010 00:05 Messages: 706 Offline
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Your custom profile sets a Min, Max and Ave Bit rate. From the bit of testing I have done if you original clips fit within these specs then the content will be copied to the output without any re-encoding (as SVRT should). However the header in the new file will be written with the profile specs by PD to describe the streams in the new file. So...in your case the video stream has not changed at all but the header info (that is read by Media Info) will have. You really don't know the "true" bit rate only what the Camcorder or PD decided to put in the header. The result is that while it is reported as changing the bit rate the stream is untouched if SVRT is used and an actual change in bit rate requires the clip to be re-encoded.

Thanks
Nathan PD 64 Bit-Win10 64 Bit-32GB RAM-80TB HDD
Sony FX6 - 500Mbps 4k/50p AVC-I HLG
Canon XF400 - 150Mbps 4k/50p AVC
GoPro Hero6 Black
Pana HS700-28Mbps 1080/50p AVC (High@L4.2)
Canon HV20-HDV 25Mbps 16:9 1440x1080/25p MPEG
JL_JL [Avatar]
Senior Contributor Location: Arizona, USA Joined: Oct 01, 2006 20:01 Messages: 6091 Offline
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You bring up a good point about the header in the file being displayed. I typically don't use MediaInfo for bitrate because of that, I use the free utility bitrate viewer for comparison when checking files. It scans the file a gives a bitrate as a function of time or frame. It has some issues too with certain files, anyone else use a similar utility that they care to share the name of?

Jeff
pjc3
Senior Member Location: Australia Joined: May 29, 2010 19:33 Messages: 247 Offline
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Quote: You really don't know the "true" bit rate only what the Camcorder or PD decided to put in the header.

Thanks
Nathan


This is the same reason encoding the same clip numerous times will result in differing bitrates and duration (albeit very small differnces) Panasonic SD9, Panasonic TM700, Panasonic SD600, GoPro HD Hero.
jmone
Senior Contributor Location: Australia Joined: Nov 26, 2010 00:05 Messages: 706 Offline
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As most of us use a Varible Bit rate any single figure should be taken with a grain of salt but they are are good approximation of what the files contains, and unless someone has modified the header or the app that wrote it is buggy so are progs like MediaInfo. If you want to see how the bit rate moves around both between and within clips then something like FFDSHOW will dynamically show you the input bitrate of the frames as they are processed (eg the attached is a snap shot only).
[Thumb - BitRate.png]
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BitRate.png
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49 Kbytes
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201 time(s)
PD 64 Bit-Win10 64 Bit-32GB RAM-80TB HDD
Sony FX6 - 500Mbps 4k/50p AVC-I HLG
Canon XF400 - 150Mbps 4k/50p AVC
GoPro Hero6 Black
Pana HS700-28Mbps 1080/50p AVC (High@L4.2)
Canon HV20-HDV 25Mbps 16:9 1440x1080/25p MPEG
JL_JL [Avatar]
Senior Contributor Location: Arizona, USA Joined: Oct 01, 2006 20:01 Messages: 6091 Offline
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As I indicated, I use bitrate viewer which provides the plot below for a sample of Canon 24Mbps footage. I actually have a lens cap on for part of the footage because I wanted to see how much Canon may drop the bitrate depending on what is being filmed. As one considers proper bounds for SVRT I have in the past looked at ranges in my Canon footage and typically about 18Mbps for min and 24Mbps for max.

It has some issues for certain footages so was looking for an alternate tool.

Jeff
[Thumb - bitrate.jpg]
 Filename
bitrate.jpg
[Disk]
 Description
bitrate plot for 2min Canon 24Mbps footage
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172 Kbytes
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225 time(s)

This message was edited 1 time. Last update was at Dec 18. 2010 13:38

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