Forum Archive Home -> Video Conversion -> AVI to MPG: Optimum bitrate?
| AVI to MPG: Optimum bitrate? | ||||||
| NDMMackay posted 2008 Oct 10 04:19 | ||||||
| If I have a CBR AVI file, is there a bitrate for the MPG file that will need the least processing? AVI file is XVid 1.0 RC2 at 2394 kbps, and I would like to be able to specify a CBR for MainConcepts encoder so that it will take the least processing time. Or is it just too content-based to be able to specify? | ||||||
| lordsmurf posted 2008 Oct 10 07:08 | ||||||
| Content-based, if retaining quality is also important. | ||||||
| jman98 posted 2008 Oct 10 08:24 | ||||||
| Welcome to the forums.
lordsmurf is correct, but to provide more info that might be helpful to a new member ... As a general rule, you will need twice the bit rate in MPEG-2 that your Xvid file has to have the same quality. Some encoders may have an option that allows you to keep the same quality on the encode, but that does NOT allow you to set the bit rate. If you care nothing about quality and are only obsessed with speed of encode, then set the bit rate lower than your Xvid file has it. Your final result won't be pretty, but it will be fast. Of course you could simply leave your computer on overnight and let it encode while you sleep and you won't care how long it takes, but some people just refuse to do that and they want everything done in 1 hour or less. If you are one of those people, then just set the bit rate low and live with the crappy quality output you get. You can either do it right or you can do it fast, but you can't do both. | ||||||
| 45tripp posted 2008 Oct 10 09:17 | ||||||
i don't see how that's helpful when the user has declared cbr intentions. next thing he'll be taking a 700k xvid and encoding to mpeg2 at 1400k cbr.... (with mainconcept no less...) if target size is not an issue, use mainconcept's consatant quality encode mode. (of course mainconcept sucks, just so you know) | ||||||
| jagabo posted 2008 Oct 10 09:37 | ||||||
| If your video is less than 1 hour and you plan to put it on one 4 GB DVD use 8000 to 9800 kbps, depending on your audio bitrate rate.
If your video is over an hour and you plan to put it on one 4 GB DVD use a bitrate calculator to determine the highest bitrate you can use. If you care about quality and will use as many DVDs as needed, or just plan to keep the file on your hard drive and don't particularly care how bit it is, use an MPEG encoder that supports constant quality encoding. Pick a quality level you are happy with and let the file come out with whatever bitrate is needed. | ||||||
| jman98 posted 2008 Oct 10 09:40 | ||||||
| 45tripp - So did you wake up deciding to be an ass from the beginning or was it a spur of the moment thing?
It's helpful because I gave him 2 choices. 1) Easy way - double the bit rate. 2) Harder way - figure out how to do a quality based encode. Your approach, to ONLY do the quality encode, is less helpful. At least I gave the guy a choice. You're all class 45tripp - not. | ||||||
| 45tripp posted 2008 Oct 10 09:46 | ||||||
wake up? who sleeps?
certainly am. once i wine and dine you, you'll know that. | ||||||
| NDMMackay posted 2008 Oct 11 01:48 | ||||||
| Question answered - content based. No easy mathematical relationship to make encoding easier (and thus faster). | ||||||
| guns1inger posted 2008 Oct 11 03:17 | ||||||
| What are you encoding for ?
If you are encoding for DVD then there are certain limitations you have to live with, which will factor into your calculations. These have already been described above, but just to consolidate, here they are again 1. You have a limited, finite amount of space (4.38 GB/8.5 GB) 2. You have a maximum allowable bitrate (10080 kbps combined video and audio), however many players struggle to play back the full rate from burn discs. 3. Encoding at the highest allowable bitrate allows for approx 65 minutes of footage on a DVD5 with good quality audio. Therefore, if your running time is longer than 65 minutes, you have to compromise. CBR can be reasonable down to around 8500 kbps for most footage, and lower if it is just talking heads or mostly static screens. If you have action, or a lot of cross fades then VBR is a better option. If you have to fit into a specific size, Quality based encoding or single pass VBR are poor options because they cannot guarantee a given target will be met. Your choice then becomes CBR and risk a quality hit, or 2 pass VBR, and accept the extra encoding time as a trade off for generally better quality. This is without even looking at the content of the video. Encoding generally hits a bottleneck at the CPU. Incremental improvements can be made with other components (extra memory, faster drives, using different physical drives for source and target footage), but ultimately, CPU is where it's at. A multi-core CPU with a multi-core aware encoder can make great gains over a single core CPU. Beyond that, not all encoders are created equal. Some are faster than others for the same or better quality. It may pay to do some comparisons on your system. One final thing to consider as a compromise. FAVC offers a middle ground that might suit your requirements. It is a Quality based, single pass encode using a quant (quality) value derived by doing a series of small encodes across samples of your entire video. The idea is that after 4 or 5 of these it finds a quality value that will give you your target file size. While this is slightly longer than a single pass encode in isolation, it is faster than a 2 pass encode, and will ensure you fit your target DVD size. It also uses the very well regarded HCEnc encoder, which is reasonably fast in it's own right. | ||||||
| lordsmurf posted 2008 Oct 12 03:14 | ||||||
You're joking, right? MC is one of the best encoders, period. It's very often used in professional settings. | ||||||
| 45tripp posted 2008 Oct 12 10:03 | ||||||
no. i never miss an opportunity to bash MC :)
just because the second is true, doesn't mean the first is. The more you push compression, the more MC shows weakness, against all other encoders. |
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