[FFmpeg-cvslog] avcodec/mpeg12dec: Don't initialize inter_scantable

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Sun Apr 28 20:56:45 2024 +0200| [1f5c64cbdc9e270495850c988e901391bc63c5d0] | committer: Andreas Rheinhardt

avcodec/mpeg12dec: Don't initialize inter_scantable

MPEG-1/2 only needs one scantable and therefore all code
already uses the intra one. So stop initializing
the inter one altogether.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1f5c64cbdc9e270495850c988e901391bc63c5d0
---

 libavcodec/mpeg12dec.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
index 851d8d9a77..9673bde764 100644
--- a/libavcodec/mpeg12dec.c
+++ b/libavcodec/mpeg12dec.c
@@ -1256,13 +1256,10 @@ static int mpeg_decode_picture_coding_extension(Mpeg1Context *s1)
     s->chroma_420_type            = get_bits1(&s->gb);
     s->progressive_frame          = get_bits1(&s->gb);
 
-    if (s->alternate_scan) {
-        ff_init_scantable(s->idsp.idct_permutation, &s->inter_scantable, ff_alternate_vertical_scan);
-        ff_init_scantable(s->idsp.idct_permutation, &s->intra_scantable, ff_alternate_vertical_scan);
-    } else {
-        ff_init_scantable(s->idsp.idct_permutation, &s->inter_scantable, ff_zigzag_direct);
-        ff_init_scantable(s->idsp.idct_permutation, &s->intra_scantable, ff_zigzag_direct);
-    }
+    // We only initialize intra_scantable, as both scantables always coincide
+    // and all code therefore only uses the intra one.
+    ff_init_scantable(s->idsp.idct_permutation, &s->intra_scantable,
+                      s->alternate_scan ? ff_alternate_vertical_scan : ff_zigzag_direct);
 
     /* composite display not parsed */
     ff_dlog(s->avctx, "intra_dc_precision=%d\n", s->intra_dc_precision);