TMPGEnc + DVD-5 bitrate settings

[john@sympatico.ca]

All DVD-9 to DVD-5 transcoding I plan to do will be about the same. No menus, just a single video and audio stream.

I want to verify a few things in deveoping an approach to setting the average and maximum bitrate for a two pass VBR in TMPGEnc (see questions in red). From the guide:

...use the 2 pass VBR mode ... Set the average bitrate as calculated before, the minimum bitrate to 0 bits/s and the maximum bitrate to 10mbit minus the bitrate of all your audio streams. Keep in mind that here a megabit is 1000kilobits, not 1024 as usual in the computer world.

1. Average bitrate

Total data for DVD is (a) 4 437 362 688 bytes (size of DVD-5).

EDIT: I had this wrong, its 4,706,074,624 bytes on a DVD-5

Extras data that can not be transcoded is (b) ~172 032 bytes (VIDEO_TS.BUP, VIDEO_TS.IFO, VTS_01_0.BUP, VTS_01_0.IFO - are they allways the same size?).

Target data to fill is (a - b) 4 705 902 592 bytes

Average bitrate (in Kbs where 1 Kbit is 1000 bits) is then,

4 705 902 592 bytes * 8 / 1000 * (time of film in seconds)

EDIT: I found one mistake I made , I did not account for the audio stream in equation 1. What I calculated was average complete(A+V) bitrate, what I want is average video bitrate which should be:

(4 705 902 592 bytes * 8 / 1000 * (time of film in seconds)) - 48

So this goes with the question below, are AC3 audio track allways the same fixed bitrate?



2. Maximum bitrate

10 Mbit/s = (a) 10 000 Kbit/s

AC3 audio is always (I think this is correct?) = (b) 48 Kbit/s

Max bitrate is (a - b) 9952 Kbits/sec


I think this is right, but if anyone sees anything that I overlooked please let me know.

John

[john@sympatico.ca]

Something wrong with my first approach so I'm trying a different method for getting the avg. bitrate for TMPGEnc transcoding.

I load the project in REMPEG2 to get the diagnostic data, then plug that into the DVD-R bitrate calculator by mhammer, but that does not give the new desired avg. bitrate for TMPGEnc, so..

(Size of new Video Stream in bytes from the bitrate calc) * 8 / 1000 * (length in seconds)

This gives a number that seems reasonable, and it fits in with the Scalefactor when comapred to the original Avg. bitrate.

So I think this is Ok, but I'm not sure about equation 2 (first post), the Max bitrate calculation, anyone got a comment on that?

[roach76]

Looks good except I think the audio is "48 KiloBYTES", so it ends up being "384 KiloBITS".

So you subtract the 384. I could be wrong.

[john@sympatico.ca]

You are correct, I had my units wrong. Thanks for pointing that out.


To recap:

Average bitrate can be calculated using data from ReMPEG2 in DVDRCalc.exe, with the equation above or by multiplying the scale factor by the original avg bitrate.

They should both give the same value.


Max bitrate is:

10 000 Kbit/s - (audio bitrate) Kbit/s

So far I've seen audio bitrates of 384 Kbit/s (see post above), and also 448 Kbps, so better be careful here.

[roach76]

A few other things.

1. Extras are not always the same size. But most of the time the difference can be minimal.

2. I think you have to divide by the number of seconds not multiply. So the more seconds the lower the bitrate. I think this is more of you just typed in the wrong symbol.

3. If you do subtitles too you have to take this into account.

[john@sympatico.ca]

Yes its is divide, just did not put all the brackets in:

[(Video Stream in bytes from the bitrate calc) * 8] / [1000 * (length in seconds)].

How does one account for the subs? Is it even necessary, I think they should be nearly insignificant?

[john@sympatico.ca]

Ok this is going to sound lame, I just found the built in bitrate calc in TMPGEnc.:stupid:

It gives numbers that are sort of close to but not equal to the numbers that I get from ReMPEG data., for example:

ReMPEG data + mhammer bitrate calc : 4941 Kbit/s

TMPGEnc: 4.33 Mbps, where 4.33 Mbps is either 4330 or 4434 Kbit/s (depending on whether you use 1000 K or 1024 K in 1 M).

So far I have been getting file sizes that are very close to the 4.7 GB limit with the ReMPEG data, so I'm happy with that.

However I am curious about this other calculation method, is it reliable?

Am I interpreting the data properly (that the resulting Mbps is Mega bits / sec and not Mega Bytes /sec etc.. etc..

[roach76]

As long as you take into account the subtitles. They are small but have an effect on the resulting bitrate. I'm not exactly sure how big they are, but IfoEdit's 'Bitrate Calculator' takes them into account.

The calcs look good, so do the units after fixing the 48 to 384 glitch. But I always usually subtract about 50 from the result to save me from a second encode.