Re: [徵求] 對MPEG影像壓縮超熟析的人
※ 引述《maby (馬畢參陸)》之銘言：
: 標題: [徵求] 對MPEG影像壓縮超熟析的人
: 時間: Tue Oct 7 16:36:33 2008
:
: 因為工作上有些問題
: 想要問問影像壓縮達人
: 關於Macroblock的問題，色差區塊和亮度區塊的問題
: 還有Encode的GOP的問題
: 感謝！
: 求救阿!
:
: --
:
: http://www.wretch.cc/album/AlbertCamus
:
: 大白
:
:
: --
: ※ 發信站: 批踢踢實業坊(ptt.cc)
: ◆ From: 219.87.154.10
: 推 billwoodss:誰找我 10/07 15:54
: → crazydj:GOP= group of picture? 10/07 15:56
: → crazydj:一般來說!不就分I，B，P frame @@? 10/07 15:56
: → maby:我要問的是稍微深入一點的問題 10/07 16:19
: → maby:色差和亮度區塊的差異和原理 10/07 16:19
你需要的應該是這個吧
http://en.wikipedia.org/wiki/Chroma_subsampling
: → maby:encoder如何去定義GOP裡面I frame與下一張I frame的距離 10/07 16:20
下面的是技術文件 網路上找不到 所以我就直接貼出來了
原文是從DVD Studio Pro User Manual出來的
There are three aspects to choosing a GOP setting: the GOP pattern, the GOP length,
and whether the GOP is “open” or “closed.”
GOP Pattern
The GOP pattern determines the ratio of P- to B-frames within a GOP. The most
common patterns used for DVD are IBP and IBBP. All three frame types do not have to
be used in a pattern; an IP pattern is also used in special circumstances.
IBP and IBBP GOP patterns, in conjunction with longer GOP lengths, produce the most
efficient encodes. Smaller GOP patterns with shorter GOP lengths work better with
video that has quick movements.
Some encoders can force I-frames to be added sporadically throughout a stream’s
GOPs. These I-frames can be placed manually by someone watching for sudden video
changes or automatically by an encoder detecting scene changes. You can place
markers in Final Cut Pro to identify specific frames to have an I-frame, either for use as a
chapter marker or to manually identify high motion areas. See “Adding Markers to Your
Video” on page 70 for more information.
The embedded MPEG encoder uses a GOP pattern of IBBP.
GOP Length
Longer GOP lengths produce more efficient encodes by reducing the number of
I-frames, but are less desirable during short-duration effects such as quick fades and
quick camera pans.
SD-Based DVDs
The maximum GOP length for SD projects is 18 frames for NTSC or 15 frames for PAL.
The minimum GOP length depends on the GOP pattern. For example, an IP pattern can
have a length as short as two frames.
The embedded MPEG encoder uses a GOP length of 15 frames for NTSC and 12 frames
for PAL SD assets.
HD-Based DVDs
Since HD projects can use both interlaced and progressive video assets, they have
different GOP length maximums.
NTSC interlaced assets: 18 frames per GOP
NTSC progressive assets: 36 frames per GOP
PAL interlaced assets: 15 frames per GOP
PAL progressive assets: 30 frames per GOP
Note: 24p assets have their GOP structure based on their display rate, not the encoded
rate. A 24p asset encoded to play in an NTSC project has a display rate of 29.97
interlaced frames (with an 18 frames per GOP maximum) or 59.94 progressive frames
(with a 36 frames per GOP maximum).
The embedded MPEG encoder uses a GOP length of 15 frames for NTSC and 12 frames
for PAL.
Open or Closed GOPs
An open GOP allows the B-frames from one GOP to look at an I- or P-frame from an
adjacent GOP. Open GOPs are more efficient, but cannot be used with multi-angle or
mixed-angle titles. A closed GOP keeps all references within itself, standing alone with
respect to other GOPs. DVD Studio Pro works with either type in single-angle titles, and
requires closed GOPs with multi-angle and mixed-angle titles.
It is important to know that the same pattern can provide different results when used
with an open or closed GOP. For example, the embedded MPEG encoder uses a closed
GOP type, and it starts its IBBP pattern with an I-frame. Other encoders using an open
GOP may start with a B-frame. In this case, starting with a B-frame is a little more
efficient; if you start with an I-frame, an extra P-frame must be added to the end (a GOP
cannot end with a B-frame).
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