Minimum and maximum bitrate

[lichtgestalt]

Hi there!

Can anyone clarify on the minimum and maximum bitrate in the DVD standard?
First up, is there a minimum bitrate specified or does it solely depend on the capabilities of your stand alone player? What do you think is save, 0, 100, 300, 500 ...?

Then there's the max. bitrate of 9.800 kbit/s (with 1 kbit == 1.000 bit watch out for apps using 1 kbit == 1.024 bit!).
In this bitrate every stream has to fit in, right? That is all audio tracks, the video and all subtitles, right?

So it is:

9.800 - 448 - 448 - x - y = 8.904 - (x+y)

for a movie with two 448 kbit/s audio tracks and two subtitles (x,y). How much bitrate has to be reserved for an average subtitle?

And: are the e.g. 448 kbit/s also based on 1 kbit == 1.000 bit? Otherwise we could put 448/1.024 = 438 kbit/s into the equation.

Thanks for any hints. Links are welcome!

lichtgestalt

[groyal]

Minimum Bitrate:

Zero, but some encoders may crash if the minimum bitrate is set below the size of the smallest GOP they can generate. 32 or 64 kbps would be a safer figure because it reserves enough bandwidth for a healthy GOP under any circumstances.

Maximum Bitrate:

This figure varies with the number of angles, but for your example the maximum is 9800, less the sum of the audio streams (896), less the sum of the subpicture streams (x+y). K=10^3 (1000) rather than 2^12 (1024).

Subpicture Streams:

The DVD spec allows up to 32 subpicture streams or a maximum stream rate of 3.36 mbps, whichever comes first. The most direct way to reserve space is to divide the available bandwidth by 32 (150 kbps) and multiply by the number of streams (2) to get 300 kbps. This is a very rough method of estimation that ignores low-level details (such as the amount of data that can be packed into a substream per GOP, the subpicture buffer size in the MPEG decoder and the actual sizes of the subpictures themselves) but for a "blind" estimate it's probably reasonably accurate.

[lichtgestalt]

Ah, thanks very much, groyal!
Then I wasn't much off after all
Though 150 kbit/s for a subtitle sounds awfully much to me...

Thanks