[FFmpeg-devel] [PATCH]Force tv range for mpeg4 gray output

[Carl Eugen Hoyos]

On Saturday 09 May 2015 11:53:13 am wm4 wrote:
> On Sat, 9 May 2015 11:12:46 +0200
>
> Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> > diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
> > index c47f5b1..162c295 100644
> > --- a/libavcodec/h263dec.c
> > +++ b/libavcodec/h263dec.c
> > @@ -48,8 +48,10 @@ static enum AVPixelFormat
> > h263_get_format(AVCodecContext *avctx) if (avctx->codec->id ==
> > AV_CODEC_ID_MSS2)
> >          return AV_PIX_FMT_YUV420P;
> >
> > -    if (CONFIG_GRAY && (avctx->flags & CODEC_FLAG_GRAY))
> > +    if (CONFIG_GRAY && (avctx->flags & CODEC_FLAG_GRAY)) {
> > +        avctx->color_range = AVCOL_RANGE_MPEG;
> >          return AV_PIX_FMT_GRAY8;
> > +    }
> >
> >      return avctx->pix_fmt = ff_get_format(avctx,
> > avctx->codec->pix_fmts); }
>
> Are you sure this doesn't overwrite color_range values read from the
> file? (I didn't check, but please make sure.)

asp and friends do not set the colour range but the user could, 
new patch attached, thank you!

> It appears to me that making GRAY full range by default wasn't such a
> good idea.

I tend to disagree.

> Also, this patch is libswscale specific

Isn't that what I said when we discussed the commit message of 
your patch and you disagreed?

> - unless you document somewhere that GRAY is in fact not just 
> like the Y plane of normal YUV formats, but is full range by default.

This wouldn't be correct: pix_fmt gray can be both full range 
or mpeg range, I just believe that if nothing is set, libswscale 
should assume full range (it has to assume something).
So far you have neither given an example of a "codec" for which 
this is different (I have, but I hope you agree these are very 
uncommon usecases) nor an example of a usecase for which FFmpeg 
can know the range and it should not be full range.

> The API is inconsistent and undocumented in this aspect.

Feel free to let libswscale print a warning if no scale was set.

Carl Eugen
-------------- next part --------------
diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
index c47f5b1..3e115eb 100644
--- a/libavcodec/h263dec.c
+++ b/libavcodec/h263dec.c
@@ -48,8 +48,11 @@ static enum AVPixelFormat h263_get_format(AVCodecContext *avctx)
     if (avctx->codec->id == AV_CODEC_ID_MSS2)
         return AV_PIX_FMT_YUV420P;
 
-    if (CONFIG_GRAY && (avctx->flags & CODEC_FLAG_GRAY))
+    if (CONFIG_GRAY && (avctx->flags & CODEC_FLAG_GRAY)) {
+        if (avctx->color_range == AVCOL_RANGE_UNSPECIFIED)
+            avctx->color_range = AVCOL_RANGE_MPEG;
         return AV_PIX_FMT_GRAY8;
+    }
 
     return avctx->pix_fmt = ff_get_format(avctx, avctx->codec->pix_fmts);
 }