Which variables make best video quality in MKVs? bitrate/profile/ref frames

[dave in or]

I have 2 videos of the same thing with different specs and I'd like some opinions on which would have the better video quality.


First file: 470 MB

• 2473 kbps video bitrate
• profile High@4.1
• 5 ref frames

Second file: 692 MB

• 3814 kbps vid bitrate
• profile High@3.1
• 2 ref frames

I'm wondering how these variables affect video quality. Does a high bitrate make up for a lower profile value or vice versa? What other factors affect video quality?

[jagabo]

Generally, a higher bitrate is higher quality.

Profiles and Levels are just labels. They're supposed to indicate the actual properties of the video but you can label any video with any profile@level you want. You can write "roses" on a box full of rocks. It's still rocks inside.

http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Profiles
http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Levels

In theory, more reference frames can lead to better quality (at the same bitrate). In reality, the encoder will rarely use more than 3 or 4, even if you enable more. Many devices are limited in the number of reference frames they support. So don't just encode everything with 16 reference frames.

But you really can't tell anything about two different encodings just from a list of the codec settings that were used to make it. Two different people may have started with two different sources and processed them differently. Many factors effect the final quality of a video. You have to actually see the it for yourself.

[aurgathor]

What are the resolutions and frame rates?

With everything else being equal, higher bitrate gives you better quality, and a few extra reference frames can't compensate for a roughly 50% higher bitrate. (assuming everything else is being equal) Note, some programs encode better than others.

[Hoser Rob]

.... some programs encode better than others.

That's for damn sure. With the exception of Handbrake and VidCoder (the latter really Handbrake with a streamlined GUI), all the encoders I've tried had an inverse relationship between the prettiness and simplicity of its interface and how well it encoded.

And some people know how to use the settings a lot better than others. I'm partial to 2 pass file size or bit rate mode. Even if it's not technically not always necessary I've gotten more consistently high quality using it.

A higher bit rate should, supposedly, indicate higher quality. But I've seen movies converted to 700Mb xvid files that were actually quite good, and ones two or three times as big that were just awful. Unwatchable.

Lower resolution caused by lower bit rate is watchable as long as it doesn't have obvious artifacts of bad encoing like pixelation or stuttering. You can tune the flaws out easily.

But signs of bad software/settings like pixelation and/or jerkiness when scenes change quickly are extremely annoying. Those can't be tuned out.

[aurgathor]

A higher bit rate should, supposedly, indicate higher quality. But I've seen movies converted to 700Mb xvid files that were actually quite good, and ones two or three times as big that were just awful. Unwatchable.

That's why the "everything else being equal"...

I've tried at least half a dozen encoders, and had to settle on mencoder because that was the one and only one that could correctly and reasonably encode everything I've tried.

Lower resolution caused by lower bit rate is watchable as long as it doesn't have obvious artifacts of bad encoding like pixelation or stuttering. You can tune the flaws out easily.

I've seen several videos (some created by me ) where everything was OK for a while, then the 'screen' just broke up into colored squares, or got completely messed up. The hardware encoder chip on my PVR-350 was very prone to the latter, for one.

[yoda313]

But I've seen movies converted to 700Mb xvid files that were actually quite good, and ones two or three times as big that were just awful. Unwatchable.

I'm sure the content has a lot to do with it. A romantic comedy with little action (on screen fast movement action that is) would not need as high a bitrate as a blockbuster summer action flick would. Something like Transformers or Lord of the Rings wouldn't look very good at the same bitrate as something like Sleepless In Seattle where there is a lot less busy movement going on in every single frame of video.

This is of course a bit of a generalization but you get my point.

[Hoser Rob]

But I've seen movies converted to 700Mb xvid files that were actually quite good, and ones two or three times as big that were just awful. Unwatchable.

I'm sure the content has a lot to do with it. A romantic comedy with little action (on screen fast movement action that is) would not need as high a bitrate as a blockbuster summer action flick would. Something like Transformers or Lord of the Rings wouldn't look very good at the same bitrate as something like Sleepless In Seattle where there is a lot less busy movement going on in every single frame of video.

This is of course a bit of a generalization but you get my point.

I'd agree to a point; some of the good 700Mb encodes I've seen were action pictures that had some pretty fast motion.

But I agree about content and style. I won't reencode my Lords of the Rings DVDs at all. It's not so much about motion as all those thousands of brilliantly designed Orcs running around.

And a lot of the Sundance type movies I like don't need super resolution.

Many of the low budget movies nowadays are shot with HD cameras, and they often seem to think they don't need lights. They do, or they're just too cheap to use them. The result often has part of the frame washed out from overlighting and another part of the same frame almost completely dark.

HD video cameras have tremendous latitude. But not that much.

I don't think it'd be possible to make those type of movie look good. Bellflower is good example of this.

[aurgathor]

But I agree about content and style. I won't reencode my Lords of the Rings DVDs at all. It's not so much about motion as all those thousands of brilliantly designed Orcs running around.

Sometimes you just don't have a choice. For viewing on a PC/TV, I normally use the unadulterated mpegs extracted from DVDs, but for my portable devices, the mpegs have to be re-encoded, no matter what. For one, none of them plays the mpegs I get off of my DVDs; in addition, their display size need to be taken into account; and lastly; they usually can't deal with arbitrarily high bitrates.

[Hoser Rob]

I don't rip to portable/mobile so that's not an issue for me.

But with a screen that small I wouldn't worry so much about bitrate or quality anyway. Unless you hold your iPad 5 inches from your nose. Which'd look pretty damn silly.

[aurgathor]

Not sure about iPads, but even my cheap 7" tablet has a 800x600 screen (NTSC DVD is 720x480) and the difference between 800 kbps and 1500 kbps material is easily visible. Of course 1500 kbps crashes it like half the time so I'll likely to settle on something like 1300 kbps.