[FFmpeg-devel] [PATCH] avcodec/h2645_vui: Interpret a degenerate SAR as unspecified.

[FFmpeg-devel] [PATCH] avcodec/h2645_vui: Interpret a degenerate SAR as unspecified.

[Giovanni Mascellani via ffmpeg-devel]

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The specification says that if either the numerator or the
denominator is zero then the SAR is to be intended unspecified.
Internally ffmpeg represents an unspecified SAR as 0/1, while
fractions with a zero denominator are not handled properly;
so we bridge the gap by replacing x/0 with 0/1.

Signed-off-by: Giovanni Mascellani <gmascellani@codeweavers.com>
---
  libavcodec/h2645_vui.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/libavcodec/h2645_vui.c b/libavcodec/h2645_vui.c
index 0e576c1563..7d01354761 100644
--- a/libavcodec/h2645_vui.c
+++ b/libavcodec/h2645_vui.c
@@ -46,6 +46,8 @@ void ff_h2645_decode_common_vui_params(GetBitContext 
*gb, H2645VUI *vui, void *l
          else if (vui->aspect_ratio_idc == EXTENDED_SAR) {
              vui->sar.num = get_bits(gb, 16);
              vui->sar.den = get_bits(gb, 16);
+            if (vui->sar.den == 0)
+                vui->sar = (AVRational){ 0, 1 };
          } else
              av_log(logctx, AV_LOG_WARNING,
                     "Unknown SAR index: %u.\n", vui->aspect_ratio_idc);
-- 
2.51.0


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[FFmpeg-devel] Re: [PATCH] avcodec/h2645_vui: Interpret a degenerate SAR as unspecified.

[Zhao Zhili via ffmpeg-devel]

> On Nov 4, 2025, at 21:37, Giovanni Mascellani via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
> 
> The specification says that if either the numerator or the
> denominator is zero then the SAR is to be intended unspecified.
> Internally ffmpeg represents an unspecified SAR as 0/1, while
> fractions with a zero denominator are not handled properly;

Is there any known issue?

> so we bridge the gap by replacing x/0 with 0/1.
> 
> Signed-off-by: Giovanni Mascellani <gmascellani@codeweavers.com>
> ---
> libavcodec/h2645_vui.c | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/libavcodec/h2645_vui.c b/libavcodec/h2645_vui.c
> index 0e576c1563..7d01354761 100644
> --- a/libavcodec/h2645_vui.c
> +++ b/libavcodec/h2645_vui.c
> @@ -46,6 +46,8 @@ void ff_h2645_decode_common_vui_params(GetBitContext *gb, H2645VUI *vui, void *l
>         else if (vui->aspect_ratio_idc == EXTENDED_SAR) {
>             vui->sar.num = get_bits(gb, 16);
>             vui->sar.den = get_bits(gb, 16);
> +            if (vui->sar.den == 0)
> +                vui->sar = (AVRational){ 0, 1 };
>         } else
>             av_log(logctx, AV_LOG_WARNING,
>                    "Unknown SAR index: %u.\n", vui->aspect_ratio_idc);
> -- 
> 2.51.0
> 
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> 

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[FFmpeg-devel] Re: [PATCH] avcodec/h2645_vui: Interpret a degenerate SAR as unspecified.

[Giovanni Mascellani via ffmpeg-devel]

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Hi,

Il 04/11/25 14:50, Zhao Zhili ha scritto:
>> The specification says that if either the numerator or the
>> denominator is zero then the SAR is to be intended unspecified.
>> Internally ffmpeg represents an unspecified SAR as 0/1, while
>> fractions with a zero denominator are not handled properly;
> 
> Is there any known issue?

I observed this problem with a bunch of video files provided by game 
OddBallers when executed with Wine/Proton. There is some more backstory 
on my first submission of this patch last year:

   https://ffmpeg.org/pipermail/ffmpeg-devel/2024-July/331835.html

Thanks, Giovanni.

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