[x264-devel] Re: Not using all pictures as reference

[Loren Merritt]

On Wed, 13 Sep 2006, Fredrik Olofsson wrote:

> On Tuesday, September 12, 2006 at 16:01:04 -0700, Loren Merritt wrote:
>> On Tue, 12 Sep 2006, Fredrik Olofsson wrote:
>>> Is it possible to configure x264 to not use all pictures as reference
>>> pircute? Like only using every other or every fourth picture as a
>>> reference picture?
>>>
>>> My application is streaming an encoded file over a network with (at
>>> encode time) unknown bandwidth. Therefore it would be useful to be able
>>> to change the stream's required bandwidth by dropping pictures that
>>> does not affect the state of the decoder. What I would like to achieve
>>> is sort of a "poor mans" bitrate-scalability.
>>
>> Turn on B-frames. To force only 1 in 4 pictures to be referenced (as
>> opposed to letting the encoder choose to maximize compression), use:
>> --bframes=3 --no-b-adapt
>
> When doing this, in combination with --ref 1, which picture will be used
> as reference? Will it be the previous I or P picture in display order? Or
> will there be some kind of reordering?

P-frames will reference the previous I- or P-frame.
B-frames will reference both the previous and following I- or P-frames in 
display order. They are then reordered so that the B-frame comes after its 
references in bitstream order.
Yes, that means that when B-frames are enabled, --ref 1 in some sense uses 
2 reference frames.

--Loren Merritt

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