Merging VCube, Руководство пользователя

Страница: 260 / 291

Appendices : MPEG Settings (MainConcept Encoder) Page 260
A standard GOP (the default settings) are 15 (maybe 18) frames long and they look like this (in the order the frames
are displayed):
B B I B B P B B P B B P B B P, B B I B B P B B P B B P B B P, ...
Here the first two B frames are dependent on both the I frame after them and the last P frame of the previous GOP.
The Broken link flag in the GOP header is there to inform decoders that some kind of action was taken such that
the preceding P frame is not present and the first 2 B frames cannot be decoded correctly (the decoder may then
ignore them). When splitting files, the files are split on a GOP boundary so that the previous P frame of the first few
B frames is not present in the new file (it is in the previous file). If the files are played one after another, and the last
P frame of the first file is kept by the decoder, the decoder can correctly decode the first few B frames of the sec-
ond file.
The Set broken link setting just allows one to specify whether the Broken link flag is set or not, and it depends on
whether you intend to play the files one after another or separately.
Write sequence/program end codes: When enabled, sequence and program end codes are written to the old file
when switching to a new file. If the files are meant to be played one after another, the streams should not be ter-
minated. This option only applies to the files that are split; it does not apply to the last (or only) file generated.
Pad VCD Audio: Some VCD burning programs require this flag to be set and some do not. VCD video packs are
2324 bytes long, but the audio packs are only 2304 bytes long. When the data is written to a VCD disk, the audio
packs are put in normal 2324 byte sectors. Some VCD burning programs deal with the extra 20 bytes themselves,
while others require the extra 20 bytes to be present. When this setting is enabled, the audio packs are padded
with 20 zero bytes so they are 2324 bytes long, if not enabled the audio packs are only 2304 bytes long. This set-
ting is only meaningful for VCD.
Write program end code: When enabled, a program end code is written at the end of the file. This setting only
applies to the last file if the splitting option is enabled, or if there is only one file generated.
Align sequence headers: When enabled, the sequence headers present in the video stream are placed at the
beginning of a PES packet, this makes it easier to find the sequence headers and the start of a GOP. When a
sequence header is aligned, it is possible that the previous video PES packet will need to be padded to make it the
correct size, so this option can consume a little of the total bitrate. This option is required for SVCD and DVD.
Add SVCD scan offset: SVCD defines some navigation information that is put into the video stream to help play-
ers jump back and forth or skip ahead easily. The info is called scan offsets, this option is normally required for
SVCD. This option also consumes a little of the video bitrate. Note: this option will be ignored if the user mux rate is
set higher than allowed for SVCD.