Re: [FFmpeg-devel] [PATCH] avcodec/photocd: allow decoding vlc with errors

[Anton Khirnov <anton@khirnov.net>]

Quoting Paul B Mahol (2023-09-27 21:53:54)
> Attached.
> 
> From 6b7e51e2b4facead9c45fb94647c85b58e6fdf22 Mon Sep 17 00:00:00 2001
> From: Paul B Mahol <onemda@gmail.com>
> Date: Wed, 27 Sep 2023 21:48:49 +0200
> Subject: [PATCH] avcodec/photocd: allow decoding vlc with errors
> 
> Also rename option that no longer works.
> Also make tables finding more robust.

Why do all these things in a single patch?

And why are there no tests for this decoder?

> Signed-off-by: Paul B Mahol <onemda@gmail.com>
> ---
>  libavcodec/photocd.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/photocd.c b/libavcodec/photocd.c
> index 07e8d460bd..a9e42bb86a 100644
> --- a/libavcodec/photocd.c
> +++ b/libavcodec/photocd.c
> @@ -277,8 +277,6 @@ static av_noinline int decode_huff(AVCodecContext *avctx, AVFrame *frame,
>              if (get_bits_left(&g) <= 0)
>                  return AVERROR_INVALIDDATA;
>              m = get_vlc2(&g, s->vlc[idx].table, s->vlc[idx].bits, 2);
> -            if (m < 0)
> -                return AVERROR_INVALIDDATA;

Shouldn't this error be at least logged? Perhaps it should still fail on
AV_EF_EXPLODE.

>              m = sign_extend(m, 8);
>              data[x] = av_clip_uint8(data[x] + m);
>          }
> @@ -389,6 +387,7 @@ static int photocd_decode_frame(AVCodecContext *avctx, AVFrame *p,
>              return AVERROR_INVALIDDATA;
>  
>          if (s->resolution == 4) {
> +            s->streampos = (AV_RB16(avpkt->data + 2048 + 1536 + 3) + 12) * 2048;

Where do these magic numbers come from? Same below.

-- 
Anton Khirnov
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