one pass or two? at DVinfo.net

Robert Bobson · September 27th, 2006, 04:52 AM

If file size doesn't matter, will a single pass CBR give you as good or better (?) quality that a two pass VBR?

Thanks

BB

Emre Safak · September 27th, 2006, 07:16 AM

Same quality, bigger size.

Mark Utley · September 27th, 2006, 10:55 AM

I've heard that when filesize doesn't matter, VBR and CBR will give you the same sized files in the end (maximum quality). CBR will encode faster because it won't be doing as much calculating.

But I could be wrong.

Emre Safak · September 28th, 2006, 07:18 AM

That is not true. In VBR you specify the average bit rate, so you can control the resulting file size. It is just that with two passes you can allocates those bits more efficiently, thereby improving the quality.

William Hohauser · September 28th, 2006, 03:13 PM

Quote:

Originally Posted by Robert Bobson

If file size doesn't matter, will a single pass CBR give you as good or better (?) quality that a two pass VBR?

Thanks

BB

Size of the project is the deciding factor. If it's a short piece, you can successfully use CBR at a high bit rate that will be as good as if not better to most VBR encodes. Above an hour of material you will be better off using VBR just so you can fit the video and keep the quality high.

Robert Bobson · September 29th, 2006, 04:34 AM

thanks for your responses ~

Thomas Smet · September 29th, 2006, 08:38 AM

Yes the quality can be better with 2 pass encoding. The reason for this is with a single pass the encoder has to do a rough estimate of what bitrate to use and it has to do it fast. A single pass may give a certain frame a bitrate of 5.5 mbits/s. A 2 pass encoder will give the first pass 5.5 mbits/s but then in the second pass realize that a 5.7 mbits/s may work better. This is a very small amount but it is higher and could mean the difference between a few macroblocks or not. This is even more true when dealing with low bitrate DVD's such as 4.5 mbits/s. At that rate every tiny bit can help.

The 2 pass also helps in that the certain frame at 5.5 may give the same amount of quality at 5.3 so that leaves a tiny bit of space left to add more bits to another section that needs it. This is why the Cinema craft encoder can do up to 8 (It may be higher) passes. Every pass it does it can really get down at nit pick the very best bitrate to use for every single frame. Every new pass the results get more accurate and fine tuned. Above 2 passes however you would really have to be a quality freak to care about the difference and I'm sure most people would never be able to tell.

September 27th, 2006, 04:52 AM	#1
Robert Bobson Major Player Join Date: Feb 2003 Location: Bay City, Michigan Posts: 585	one pass or two? If file size doesn't matter, will a single pass CBR give you as good or better (?) quality that a two pass VBR? Thanks BB

September 27th, 2006, 10:55 AM	#3
Mark Utley Major Player Join Date: Mar 2004 Location: Toronto, ON, Canada Posts: 479	I've heard that when filesize doesn't matter, VBR and CBR will give you the same sized files in the end (maximum quality). CBR will encode faster because it won't be doing as much calculating. But I could be wrong. __________________ Mark Utley

September 27th, 2006, 07:16 AM	#2
Emre Safak Trustee Join Date: Feb 2004 Location: Brookline, MA Posts: 1,447	Same quality, bigger size.

September 28th, 2006, 07:18 AM	#4
Emre Safak Trustee Join Date: Feb 2004 Location: Brookline, MA Posts: 1,447	That is not true. In VBR you specify the average bit rate, so you can control the resulting file size. It is just that with two passes you can allocates those bits more efficiently, thereby improving the quality.

September 29th, 2006, 04:34 AM	#6
Robert Bobson Major Player Join Date: Feb 2003 Location: Bay City, Michigan Posts: 585	thanks for your responses ~

September 29th, 2006, 08:38 AM	#7
Thomas Smet Trustee Join Date: Mar 2004 Location: Milwaukee, WI Posts: 1,719	Yes the quality can be better with 2 pass encoding. The reason for this is with a single pass the encoder has to do a rough estimate of what bitrate to use and it has to do it fast. A single pass may give a certain frame a bitrate of 5.5 mbits/s. A 2 pass encoder will give the first pass 5.5 mbits/s but then in the second pass realize that a 5.7 mbits/s may work better. This is a very small amount but it is higher and could mean the difference between a few macroblocks or not. This is even more true when dealing with low bitrate DVD's such as 4.5 mbits/s. At that rate every tiny bit can help. The 2 pass also helps in that the certain frame at 5.5 may give the same amount of quality at 5.3 so that leaves a tiny bit of space left to add more bits to another section that needs it. This is why the Cinema craft encoder can do up to 8 (It may be higher) passes. Every pass it does it can really get down at nit pick the very best bitrate to use for every single frame. Every new pass the results get more accurate and fine tuned. Above 2 passes however you would really have to be a quality freak to care about the difference and I'm sure most people would never be able to tell.