[FFmpeg-devel] [PATCH] avcodec/mpegvideo_enc: Don't copy non-existent padding

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

The allocated buffer of an AVFrame need not be height * linesize
big. In case there is padding between lines, the last line need
not have this padding. Pathological examples exist with height == 1
(where linesize is not really meaningful); non-pathological examples
are produced by the separatefields filter, which simply offsets
the pointers and doubles linesize, so that the frame created from
the bottom field has only height - 1 lines with padding (containing
the top field) and one line without padding.

The mpegvideo encoders sometimes copy the input frames for padding/
alignment reasons and when doing so, there is a fast path in which
everything is copied with one memcpy() of height * linesize. And
this is wrong as explained above. Use av_image_copy_plane() instead
of our ad-hoc code for copying.

Fixes ticket #10754 (discovered by Zeng Yunxiang).

(The above discussion presupposes linesize > 0 and would need some
adaptation for negative linesizes; the code removed seems even more
buggy for negative linesizes.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
1. One could also use av_image_copy().
2. The "direct" (non-copy) path only ensures a height mod 16, yet
the non-direct mode sometimes pads to 32 (for non-progressive mpeg2).
Seems fishy.

 libavcodec/mpegvideo_enc.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/libavcodec/mpegvideo_enc.c b/libavcodec/mpegvideo_enc.c
index 6d2d417454..fac9bb7ae7 100644
--- a/libavcodec/mpegvideo_enc.c
+++ b/libavcodec/mpegvideo_enc.c
@@ -36,6 +36,7 @@
 #include <stdint.h>
 
 #include "libavutil/emms.h"
+#include "libavutil/imgutils.h"
 #include "libavutil/internal.h"
 #include "libavutil/intmath.h"
 #include "libavutil/mathematics.h"
@@ -1201,28 +1202,16 @@ static int load_input_picture(MpegEncContext *s, const AVFrame *pic_arg)
                 int w = s->width  >> h_shift;
                 int h = s->height >> v_shift;
                 const uint8_t *src = pic_arg->data[i];
-                uint8_t *dst = pic->f->data[i];
+                uint8_t *dst = pic->f->data[i] + !s->avctx->rc_buffer_size * INPLACE_OFFSET;
                 int vpad = 16;
 
+                av_image_copy_plane(dst, dst_stride, src, src_stride, w, h);
+
                 if (   s->codec_id == AV_CODEC_ID_MPEG2VIDEO
                     && !s->progressive_sequence
                     && FFALIGN(s->height, 32) - s->height > 16)
                     vpad = 32;
 
-                if (!s->avctx->rc_buffer_size)
-                    dst += INPLACE_OFFSET;
-
-                if (src_stride == dst_stride)
-                    memcpy(dst, src, src_stride * h);
-                else {
-                    int h2 = h;
-                    uint8_t *dst2 = dst;
-                    while (h2--) {
-                        memcpy(dst2, src, w);
-                        dst2 += dst_stride;
-                        src += src_stride;
-                    }
-                }
                 if ((s->width & 15) || (s->height & (vpad-1))) {
                     s->mpvencdsp.draw_edges(dst, dst_stride,
                                             w, h,
-- 
2.34.1

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