[FFmpeg-devel] [PATCH] libx264: support for BUILD >= 63

Robert Swain robert.swain
Wed Sep 17 19:20:38 CEST 2008

2008/9/17 Michael Niedermayer <michaelni at gmx.at>:
> On Wed, Sep 17, 2008 at 04:40:54PM +0100, Robert Swain wrote:
>> 2008/9/17 Daniel G. Taylor <dan at programmer-art.org>:
>> > On Wed, 2008-09-17 at 09:44 -0500, Dion Galbreath wrote:
>> >> The only worry I have is that when you use the latest x264 the bitrate
>> >> might as well not even be there since it's not really used.. it will
>> >> give you whatever it feels like. I have since been using  version 803
>> >> which works great however these new changes now effectively kill that
>> >> from working, and your forced to go back to new builds of x264 which the
>> >> bitrate once again becomes a useless property...   any chance that that
>> >> part of ffmpeg can be fixed, I'm guessing that at the time v803 was
>> >> around ffmpeg was coded to use those properties but since 804 to now
>> >> that property had changed? I never looked much into it, it's just hard
>> >> to appreciate a fix in ffmpeg that degrades such a major encoding
>> >> function as bitrate.....
>> >
>> > I've noticed that qmax now defaults to around 31, which means you cannot
>> > achieve low bitrates that degrade quality beyond q=31. You can fix this
>> > by passing -qmax 51, which should allow any bitrate regardless of how
>> > bad the quality will be.
>> >
>> > I've had a quick look through the code to find where the lower qmax
>> > value could be set but haven't had any luck. Anybody know anything about
>> > this?
>> This is an issue of reusing variables for all codecs. Prior to h.264,
>> I think all quantiser ranges were 1-31. The qmax variable was
>> naturally reused but its default value remains as 31 despite having
>> its maximum possible value increased to 51.
>> Regardless, there are a number of other poor defaults in FFmpeg that
>> make using simple command lines for x264 and obtaining a good quality
>> output not possible. However, we do have the possibility of using
>> presets in FFmpeg now.
>> Presets:
>> http://rob.opendot.cl/index.php/2008/07/23/lc-aac-and-sbr-amr-nb-floating-point-presets/
>> (Note: rc_eq has been removed from the public x264 API and no longer
>> needs to be specified at all. Manually specify -threads 0 for
>> automatic choice of the number of threads x264 should use.)
> what about putting the x264 preset files in svn?

Can do. Shall I make a presets dir and put them in there? Or ffpresets
or something like that?


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