@@ -751,7 +751,7 @@ static int apng_encode_frame(AVCodecContext *avctx, const AVFrame *pict,

                 if (last_fctl_chunk.dispose_op == APNG_DISPOSE_OP_BACKGROUND) {

                     for (y = last_fctl_chunk.y_offset; y < last_fctl_chunk.y_offset + last_fctl_chunk.height; ++y) {

-                        size_t row_start = s->last_frame->linesize[0] * y + bpp * last_fctl_chunk.x_offset;

+                        size_t row_start = diffFrame->linesize[0] * y + bpp * last_fctl_chunk.x_offset;

                         memset(diffFrame->data[0] + row_start, 0, bpp * last_fctl_chunk.width);

                     }

                 }

@@ -926,7 +926,7 @@ static int encode_apng(AVCodecContext *avctx, AVPacket *pkt,

                 uint32_t y;

                 uint8_t bpp = (s->bits_per_pixel + 7) >> 3;

                 for (y = s->last_frame_fctl.y_offset; y < s->last_frame_fctl.y_offset + s->last_frame_fctl.height; ++y) {

-                    size_t row_start = s->last_frame->linesize[0] * y + bpp * s->last_frame_fctl.x_offset;

+                    size_t row_start = s->prev_frame->linesize[0] * y + bpp * s->last_frame_fctl.x_offset;

                     memset(s->prev_frame->data[0] + row_start, 0, bpp * s->last_frame_fctl.width);

                 }

             }