7.1

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Burn to Disc (VCD, SVCD, DVD)
Variable Modes (VBR)
A variable bit rate (VBR) is the answer when you have frame sequences with different degrees of com-
plexity where the rate and, therefore, the compression fluctuates around an Average. When you specify a
Maximum value, you can encode particularly fast (high motion) or complex (high detail) scenes at a
higher bit rate and thereby increase the quality of the visual impression.
The Av era g e can be no higher than the maximum value currently set. Note that the average value has a
greater influence on data throughput than the maximum value.
 Storage VBR (StorVBR) -
This mode mostly keeps the bit rate at or slightly below the selected average value, which it does
not exceed. Recommended for most applications. In contrast to CBR both VBR modes do not
encode “empty” bits (what‘s called zero bit stuffing).
 Statistical VBR (StatVBR) -
Select an average value and a maximum value. Generally recommended for DVD and any record-
ing longer than 15 minutes. This mode supports only 4:2:0 chroma sampling and long GOPs
(M = 3 and N = 15).
The disadvantage of VBR, however, is that the fluctuating average makes it impossible to accurately pre-
calculate the size.
GOP
GOP (Group of Pictures) relates to the sequence of I, P and B frames used for MPEG compression. I
frames (intra-codec picture) store the contents of an image at their full resolution; P and B frames each
store changes in the image that occur between I frame and I frame. P stands for forward Predictive pic-
tures and B stands for Bi-directional pictures. GOPs are very basic elements of an MPEG stream. A GOP
can have the following appearance:
I-B-B-P-B-B-P-B-B-P-B-B-P-B-B-I
I-frame only
In the case of the Elementary Stream and Program Stream Destination formats: Click this option to
export a stream consisting entirely of I-frames. Afterwards, the N and M value can no longer be changed.
GOP Size
The GOP size (aka N value) is measured from I frame to I frame. The shorter the GOP, the more I frames
with relation to the overall MPEG sequence; the longer the GOP, the fewer the I frames in an MPEG
stream. Short GOPs require a higher bit rate because more I frames also means more data.
Keep this in mind if you want to modify the GOP.