[Ffmpeg-devel] ASP/AVC defaults

Robert Swain robert.swain
Wed Dec 7 16:27:30 CET 2005


>> gop_size
>> current = 12 (... in ffmpeg.c which overwrites 50 in utils.c)
>> proposed = 10 * framerate (for ASP and AVC)
> not ok, mpeg doesnt allow >132 updates (inter MBs) or so, either check 
> that
> there are not to many colocated inter MBs or set the default GOP <132
> and yes iam aware everyone uses 300frame gops in mpeg4 but the defaults
> should not violate the spec, not to mention that theres a reason why
> that 132 limit is in there ...

That's fair. I don't want to violate the specs either and that limitation 
had slipped my mind. I'll look into checking that, thank you.

>> It should be apparent that there is the problem of different default 
>> value
>> requirements sharing the same parameters. I could add new parameters for
>> each codec as necessary (say -asp_qmin and so on) or I could design some 
>> new
>> method for handling defaults dependent on which codec is selected. I 
>> don't
>> know which way is better or if there are other, better methods that I
>> haven't thought of, but I would appreciate your input to select the most
>> acceptable method before I begin.
> IMHO -asp_qmin is a silly idea

I agree, but it is an option. :) In x264, knowing if the parameter had been 
changed at the command line is enough as the x264 defaults are set before 
passing any other params to it. I'll see if I can concoct any reasonable 
codec dependent default parameter method.

> you should also be carefull not to break any regression tests
> (update regression.sh to avoid checksum changes)

OK, thank you.

As you haven't commented on the other suggestions, am I to assume that you 
think they are OK? :)


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