[Ffmpeg-devel] [PATCH] AVOption defaults sync

Panagiotis Issaris takis.issaris
Thu Sep 14 15:08:51 CEST 2006


Op donderdag 14 september 2006 15:01, schreef Baptiste Coudurier:
> [...]
> >>> The attached patch synchronizes the defaults specified in the AVOptions[] array 
> >>> to the defaults specified in the ffmpeg.c global static variabels. I took the
> >>> ones specified in ffmpeg.c as the new ones for AVOptions, as this preserves the 
> >>> current behavior. Regression tests pass.
> >> looks ok though i think that we should eventually change the default of 
> >> 12frame gop and 200kbit its probably not what most users would want
> > Does the "eventually" imply that I can commit the patch as is, and
> > that the defaults can be modified in a follow-up patch?
> > 
> > If so, would 800kbit and 15 frame GOP be more in line with what users
> > want? Or should I post to ffmpeg-users and see what is being most
> > commonly used? :)
> > 
> 12 is actually much used in MPEG-2 PAL since it's around 25/2 s, 15 is 
> more used in NTSC (30/2), DVD specs requires the gop not to be > 18, 
> MPEG-4 should use a much larger gop size though.
Well, the MPEG-4 codec is used by default, so I would assume it would
be most interesting to give it a "good" value for MPEG-4 encoding, and
ignore f.e. the DVD specs. If one wants DVD compliance, one will most
likely use the -target (pal|ntsc)-dvd anyway. Remains to be seen what
a "good" GOP size for MPEG-4 would be... :)

I vaguely recall someone doing tests altering various libavcodec encoding 
parameters and comparing the resulting visual quality and/or PSNR. I could
search and have a look at that, but I'm not sure if it is still relevant. 
I think I saw this webpage some years ago, and FFmpeg's MPEG-4 encoding might 
have changed considerably. Would it be a good idea to look at it, or would
it not be relevant anymore?

With friendly regards,

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