[FFmpeg-devel] [PATCH] vaapi_vp8: Use VP8_MAX_QUANT instead of magic number

[Michael Niedermayer]

On Thu, Feb 16, 2017 at 08:45:33PM +0000, Mark Thompson wrote:
> ---
> On 16/02/17 20:15, Michael Niedermayer wrote:
> > On Thu, Feb 16, 2017 at 05:11:54PM +0000, Mark Thompson wrote:
> >> On 16/02/17 16:20, Michael Niedermayer wrote:
> >>> Its used elsewhere for 2^p-1 cliping
> >>>
> >>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >>> ---
> >>>  libavcodec/vaapi_encode_vp8.c | 6 +++---
> >>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/libavcodec/vaapi_encode_vp8.c b/libavcodec/vaapi_encode_vp8.c
> >>> index 4a1c85e66c..3d3831c46d 100644
> >>> --- a/libavcodec/vaapi_encode_vp8.c
> >>> +++ b/libavcodec/vaapi_encode_vp8.c
> >>> @@ -161,12 +161,12 @@ static av_cold int vaapi_encode_vp8_configure(AVCodecContext *avctx)
> >>>      VAAPIEncodeContext     *ctx = avctx->priv_data;
> >>>      VAAPIEncodeVP8Context *priv = ctx->priv_data;
> >>>  
> >>> -    priv->q_index_p = av_clip(avctx->global_quality, 0, 127);
> >>> +    priv->q_index_p = av_clip_uintp2(avctx->global_quality, 7);
> >>>      if (avctx->i_quant_factor > 0.0)
> >>> -        priv->q_index_i = av_clip((avctx->global_quality *
> >>> +        priv->q_index_i = av_clip_uintp2((avctx->global_quality *
> >>>                                     avctx->i_quant_factor +
> >>>                                     avctx->i_quant_offset) + 0.5,
> >>> -                                  0, 127);
> >>> +                                  7);
> >>>      else
> >>>          priv->q_index_i = priv->q_index_p;
> >>
> >> IMO this makes the code less readable, not more.  It doesn't really matter to anything, though, so commit it if you really want to.
> >>
> >> (If this is mainly objecting to the magic number being visible there then please do introduce a constant to hide it rather than making the constant smaller - VP8_QINDEX_RANGE, say, to match <https://tools.ietf.org/html/rfc6386#section-14.1>.)
> > 
> > I just suggested it because its the only case we have in the codebase
> > that matches this:
> > git grep -E 'av_clip *\(.*, *0 *, *(3|7|15|31|63|127|255|511|1023|2047|4095|8191|16383|32767|65535|131071|262143|524287|1048575|2097151|4194303|8388607|16777215|33554431|67108863|134217727|268435455|536870911|1073741823) *\)'
> > 
> > If we dont use the more optimized code everywhere then finding
> > cases where it makes a difference and isnt used is harder and not
> > something i would attempt.
> > 
> > i can also move this into fate-source
> > (there it might even be possible to keep track of exceptions)
> > but previous additions to fate-source had opposition, so iam not
> > doing that unless theres some positive feedback in that direction
> > first ...
> 
> That does make a lot of sense; I would be in favour of having automated checks like that in fate-source.
> 
> To remove the issue here, how about this patch instead?  The constant already exists in the VP8 header, so we can just use it from there.
> 
> 
>  libavcodec/vaapi_encode_vp8.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

patch LGTM

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20170217/73dbb683/attachment.sig>