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

[Paul B Mahol <onemda@gmail.com>]

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Attached.

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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.

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;
             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;
             interp_pixels(ptr, p->linesize[0], img_info[4].width, img_info[4].height);
             interp_lines (ptr, p->linesize[0], img_info[4].width, img_info[4].height);
 
@@ -396,7 +395,7 @@ static int photocd_decode_frame(AVCodecContext *avctx, AVFrame *p,
                 if ((ret = read_hufftable(avctx, &s->vlc[n])) < 0)
                     return ret;
             }
-            s->streampos = (s->streampos + 2047) & ~0x3ff;
+            s->streampos = (AV_RB16(avpkt->data + 2048 + 1536 + 3) + 14) * 2048;
             if (decode_huff(avctx, p, 4, 4) < 0)
                 return AVERROR_INVALIDDATA;
         }
@@ -447,7 +446,7 @@ static av_cold int photocd_decode_close(AVCodecContext *avctx)
 #define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
 
 static const AVOption options[] = {
-    { "lowres",  "Lower the decoding resolution by a power of two",
+    { "reduction", "Lower the decoding resolution by a power of two",
         OFFSET(lowres), AV_OPT_TYPE_INT,  { .i64 = 0 }, 0, 4, VD },
     { NULL },
 };
-- 
2.42.0


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