[Libav-user] Closed GOP structure problem
i.like.privacy.too at gmail.com
Thu Jan 1 06:46:04 CET 2015
On 12/19/2014 05:08 PM, Valentin Noël wrote:
> Hi to all,
> I would like to encode MPEG-2 video with closed GOP of 12 frames, and
a structure like IBBPBBPBBPBB.
> However, the result is a GOP of 10 frames IBBPBBPBBP, with two
missing B frames.
The meaning of "closed GOP" is that it can be decoded on its own without
help from other GOPs.
a B frame is between two non-B frames, e.g. your first B is between your
first I and your first P, the 3rd B is between the first P and the second P.
Now, if you had a B at the end, which two frames would it be between?
There is no I or P frame that follows it. So in a closed GOP the last
frame cannot be a B frame.
Also, it is important to remember that the presentation and decoding
order are different. e.g. the presentation is what you wrote:
But the decoding must (because B needs both previous I/P and next I/P) be:
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