[FFmpeg-devel] Small modifcation to libavformat/dvbsubdec.c

[Michael Niedermayer]

On Mon, Sep 16, 2013 at 08:16:53PM +0100, JULIAN GARDNER wrote:
> 
> 
> >________________________________
> > From: Michael Niedermayer <michaelni at gmx.at>
> >To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org> 
> >Sent: Monday, 16 September 2013, 18:09
> >Subject: Re: [FFmpeg-devel] Small modifcation to libavformat/dvbsubdec.c
> > 
> >
> >On Mon, Sep 16, 2013 at 08:46:39AM +0100, JULIAN GARDNER wrote:
> >> 
> >> 
> >> >________________________________
> >> > From: JULIAN GARDNER <joolzg at btinternet.com>
> >> >To: FFmpegdevelopment discussions and patches <ffmpeg-devel at ffmpeg.org> 
> >> >Sent: Wednesday, 4 September 2013, 23:51
> >> >Subject: Small modifcation to libavformat/dvbsubdec.c
> >> > 
> >> >
> >> >
> >> >diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
> >> >index 955925a..faa510a 100644
> >> >--- a/libavcodec/dvbsubdec.c
> >> >+++ b/libavcodec/dvbsubdec.c
> >> >@@ -1015,9 +1015,9 @@ static void dvbsub_parse_clut_segment(AVCodecContext *avctx,
> >> > 
> >> >         if (depth & 0x80)
> >> >             clut->clut4[entry_id] = RGBA(r,g,b,255 - alpha);
> >> >-        if (depth & 0x40)
> >> >+        else if (depth & 0x40)
> >> >             clut->clut16[entry_id] = RGBA(r,g,b,255 - alpha);
> >> >-        if (depth &
> >> 0x20)
> >> >+        else if (depth & 0x20)
> >> >             clut->clut256[entry_id] = RGBA(r,g,b,255 - alpha);
> >> >     }
> >> >     }
> >> >
> >> >
> >> >Just so it adheres to spec. Page 25 of ETS300743 V1.2.1, page 25.
> >> >
> >> >2-bit/entry_CLUT_flag: If set to '1', this indicates that this CLUT value is to be loaded into the identified entry of the
> >> 2-bit/entry CLUT.  
> >> >4-bit/entry_CLUT_flag: If set to '1', this indicates that this CLUT value is to be loaded into the identified entry of the
> >> 4-bit/entry CLUT. 
> >> >8-bit/entry_CLUT_flag: If set to '1', this indicates that this CLUT value is to be loaded into the identified entry of the
> >> 8-bit/entry CLUT. 
> >> >NOTE 1: Only one N-bit/entry_CLUT_flag shall be set to 1 per CLUT_entry_id and its associated Y-, Cr-, Cb- and
> >> T -values. 
> >> >joolz
> >> >
> >> Any comment on this, will it be pushed?
> >
> >what does this patch fix ?
> >please provide a testcase or if it fixes spec compliance a quote of
> >the spec saying that if multiple bits are set this new behavior is
> >to be used.
> >
> >You quote just a part of the spec that says that the affected case
> >shall not occur. why would a change in behavior for a case that lies
> >outside the spec be a matter of spec adherence ?
> >I surely am missing something here ...
> >
> >[...]
> >-- 
> >Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> >
> >No human being will ever know the Truth, for even if they happen to say it
> >by chance, they would not even known they had done so. -- Xenophanes
> >
> >_______________________________________________
> >ffmpeg-devel mailing list
> >ffmpeg-devel at ffmpeg.org
> >http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> 
> This patch fixes a non corfmance to the DVB Subtitle spectications, as i pointed out in my mail.
> 
> No i cannot provide a non working one as this would break the specification. All DVB Streams adhere to this specification, find me one that fails and I will bow to your interpretation.
> 
> 
> I think English is not you mother tongue but 
> 
> 
> "NOTE 1: Only one N-bit/entry_CLUT_flag SHALL be set to 1 per CLUT_entry_id and its associated Y-, Cr-, Cb- and T -values." 
> 
> 
> SHALL (from dictionary.com)
> 3.(in laws, directives, etc.) must; is or are obliged to: The meetings of the council shall be public.  
> 
> OBLIGED (from dictionary.com)
> 1.to require or constrain, as by law, command, conscience, or force of necessity.
> 
> 
> CONSTRAIN (from dictionary.com)
> 1. to force, compel, or oblige
> 
> 
> To a native english speaker this is clear, You can only set a one of the 3 bits.
> 
> 
> So its either ffmpeg follows spec, or ffmpeg follows Michaels interpretation of the spec.

Can someone else please look at the patch and the quoted text from the
spec and comment if this patch is correct and fixes a spec non
conformance issue or not.

Thanks

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

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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